This board needs more activity. So quit lurking around and post those games that are honored to fill your hard drive.
 
Screenies are always welcome, but of course if you feel lazy you can just list em.

Counter-Strike: Source
Counter-Strike 1.6
Team Fortress 2
Team Fortress Classic
Fallout 3
Fallout New Vegas
Duke Nukem Forever
StarCraft 2
Amnesia Dark Descent
Modern Warfare 2
Black Ops
Bad Company 2
Crysis 2
Dragon Age: Origins/Awakening
Dragon Age 2 
Beyond Good and Evil
Chronicles of Riddick
Clive Barker's Jericho
Majesty 2
Left 4 Dead 2
Mass Effect
Mass Effect 2 
Portal 2
Civilization 5
COD W@W
 WoW (Inactive account though)

Think that's it.

Wish I had that much space on my HDD. Or maybe I should free some space by deleting those... never mind.

You need at least a 1TB man! I'm still only about half full on my mine.

As for games installed... everything that I own on steam. Jamestown being the most recent acquisition.

Mount & Blade Warband
Age of wonders : Shadow Magic
GTA
GTA III
Eufloria
Hitman 1
Divine Divinity
Heroes of Might and Magic IV
Lords of Magic
Max Payne 2
Arcanum - of steamworks and magic obscura
Grim Fandango
Diablo 2
Torchlight
Machinarium
Recettear
Osmos
Uplink
Darwinia
VVVVVVV
Super meat boy
Plants vs Zombies
Bejeweled 3
Comandos
XCOM : UFO defense
Starcraft Broodwar
ES II Daggerfall
ES III Morrowind
Battle for Wesnoth
 
Yeah I have a problem...... Also the most observant of you will notice that they are all (except for M&B) very old games/small indie games, that's because all I have PC wise is a crappy notebook.
 
Also important to note the I barely play 80% of this list.

I just did a format a few days ago, so not as many as I used to. Right now I got:
 

• Hitman: Blood Money
• Total War: Shogun 2
• Dungeon Siege
• Dungeon Siege 2
• Dungeon Siege 3 - Preloading at the moment, but still counts.
  
• Gothic 3
• Grand Theft Auto: Episodes from Liberty City
• Grotesque Tactics: Evil Heroes
• King Arthur - The Role Playing Game
• Left 4 Dead 2
• Rise of Nations: Thrones and Patriots
  
• Saints Row 2
• Spiral Knights
• Terraria
• Trine
  

I'm more into emulating my old PS2 favorites than anything I have installed. //Puzzle Quest 2 seems to have dropped off the list, oh well.

Oldies but goldies, right.
 
So here's what I have on my humble disk:
 
Call of Duty 2
Call of Duty 4
Call of Duty: WaW
Call of Duty: MW2
Call of Duty: Black Ops
Company of Heroes: Tales of Valor
StarCraft II
Age of Empires 3 + 2 expansions
GTA IV
GTA: Episodes From Liberty City
Stronghold Crusader
DiRT 3

Borderlands  
KOTOR 1 
Fallout 3
Fallout New Vegas  
Duke Nukem Forever 
The Sims 3 
Rome Total War 
Sim City 4
Need for Speed Most Wanted 
Luxor HD 
NES Emulator

Borderlands, Dirt 1, Grid, NFS Shift, Transformers WFC, ME2, Blur, UT3, Peggle, Lumines, Puzzle Quest. I think that's all of them.

Deus Ex
Age of Empires 1-3
KOTOR 1 & 2  
Homeworld 1 & 2
Porn  :(

• Alien Swarm
• Borderlands
• Braid
• Dead Space
• Fallout: NV
• Far Cry 1 and 2
• Jamestown
• Left 4 Dead 2
• Magic the Gathering - Duels of the Planeswalkers (original and 2012)
• Magicka
• Mass Effect
• The Misadventures of PB Winterbottom
• Monday Night Combat
• On the Rain-Slick Precipice of Darkness (episode 2)
• Plants vs Zombies: GOTY
• Portal
• Prince of Persia: Sands of Time
• Puzzle Quest
• Resident Evil 5
• Sam and Max (Seasons 1,2, and 3)
• Shank
• Street Fighter IV
• Super Meat Boy
• Swords and Soldiers HD
• Team Fortress 2
• Rainbow Six Vegas 2
• Splinter Cell: Chaos Theory
• Splinter Cell: Conviction
• Torchlight
• Trine
• VVVVV

• Aaah reckless disreguard for gravity
• Aquaria
• Audiosurf
• Beat Hazard
• Bit.Trip RUNNER
• Braid
• Bully: Scholarship Edition
• Defense Grid: The Awakening
• Deus Ex
• Europa Universalis 3 + all expansions
• Everyday Genius: Square Logic
• Far Cry 2
• Flora's Fruit Farm
• Hitman: Blood Money
• Civilization 4
• L4D2
• Magicka
• Majesty 2
• Metro 2033
• P.B. Winterbottom
• Mount & Blade: Warband
• Neverwinter Nights 2
• Plants Vs. Zombies
• Portal 2
• Puzzle Quest
• Recettear
• Stalker: Clear Sky
• Shatter
• KOTOR
• Super Meat Boy
• Tales of Monkey Island 1
• TF2
• Trackmania Nations
• Trials 2
• Trine
• The Void
• The Witcher 2
• VVVVVV
• Zeno Clash
• Sid Meier's Alpha Centauri
• The Precursors
• Baldur's Gate 1 & 2
• Planescape: Torment
• Digital: A Love Story
• don't take it personally, babe, it just ain't your story
• The Sims 3
• Arcanum
• Fallout 1 & 2
• Psychonauts
• Stronghold
• Syberia
• The Guild
• The Longest Journey
• Machinarium
• GTA: Vice City
• Warcraft 3
• REAL LIVES 2007 DOG.

man no wonder I only have 100 gigs left on this 1tb drive

I don't have a very big hard-drive but I had a lot more on here than I thought:

• Bejeweled 2: Deluxe
• Counter-Strike: Source
• Dark Void Zero
• Digital: A Love Story
• Garry's Mod
• Guild Wars (including Factions and Nightfall expansions)
• Halo: Combat Evolved
• Maplestory
• The Marriage
• Passage
• Peggle Nights
• Plants vs. Zombies: Game of the Year Edition
• Poker Night At the Inventory
• Revenge of the Titans
• Sid Meier's Civilisation IV
• Sid Meier's Pirates
• The Sims 2 (including University and Seasons expansions)
• Spore
• Starcraft II
• Super Meat Boy
• Team Fortress 2
• Tibia
• World of Warcraft (including Burning Crusade and Wrath of the Lich King expansions)
• The default Windows XP games

Lots.

Lol, I totally suck among you guys with my small list.

• Mount and Blade: Warband.
• Dungeon Siege.
• Morrowind.
• The Black Mirror.
• Beat Hazard.
• TrackMania Nations Forever.
• VVVVVV.
• Medieval II Total War.
• Sam and Max 202.

I got a pretty small list too. One thing I noticed in the past few years is that I have begun to enjoy PC gaming once again. 
 
So these are currently on my hard drive, hopefully with more to come as the cash flows bigger!
 
- Starcraft 2
- Plants vs Zombies
- Mass Effect 2 (late to the party, baby, I know, but fuck playing it on PS3!)
- Torchlight
- Titan Quest (missed this gem when first came out. Very respectable dungeon crawler)
- Civ IV - need to upgrade to Civ V, but for now, IV is still excellent.
- Medieval II Total War
- Rome Total War Gold Edition
- Mini Ninjas
- Dungeon Siege & DS Legends of Aranna
 
As I said, this list will grow in the near future!

With an itty bitty HDD.  
 
StarCraft II 
Diablo II + LoD (always installed...always) 
Alpha Protocol 
NWN2 + Expansions 
STALKER: Call of Pripyat + Complete Mod
Puzzle Agent 
Melty Blood Actress Again (don't own a Japanese PS2, therefore emu) 
Guilty Gear XX #RELOAD 
SF3: 3S (no DC or cab, so again...emu)

• Dawn of War 2: Retribution
  
• Darksiders
• Splinter Cell
• Splinter Cell: Chaos Theory
• Splinter Cell: Double Agent
• Lara Croft and the Guardian of Light
• Magicka
• Prince of Persia: The Forgotten Sands
• Red Faction: Guerrilla
• Rayman 2: The Great Escape
  

• Assasins Creed II
• Super Meat Boy
• Crysis 2
• Back to the Future ep 1 - 4
• Bejeweld3
• Fable 3
• MicroVolts
• Alice Madness Returns
• Borderlands GOTY
• The Cat and the Coup
• Dirt 2
• Killing Floor
• Portal
• Team Fortress 2
• Trine

More than I should, but I'd have more if I could get Steam to reliably install across my other hard drives. My 750GB main is full of 500GB of games, but the other ~3.5TB I have on my computer are largely unused (except for media).

Non Steam games:

• Witcher 2
• Neverwinter Nights Diamond
• Heroes of Might and Magic 3
• Diablo 2
• Drakensang
• Chronicles of Riddick
• Guild Wars
• Two Worlds
• LotR Online
• Planescape Torment
• Baldur's Gate 2
• Shadowrun
• Viva Pinata

And I'm probably forgetting a few.

All 130 or so of my Steam games.

• All the games that I've bought on Steam, plus starcraft:
• 1..2..3..kick it
• AAAaAAAAaAAAA !!!- A reckless disregard for gravity
• BFBC2
• Borderlands
• Burnout Paradise
• CoD Blops
• Crysis
• Deus Ex GOTY
• Fallout New Vegas
• Far Cry 2
• Frozen Synapse
• GTA Vice City
• Hitman 2:blood assassin
• Hitman Blood Money
• Hitman Codename 47
• Jamestown
• Kane and Lynch 2
• L4D2
• Magicka
• NBA 2k11
• Poker Night at the Inventory
• Portal
• Receattear
• Red Faction:Guerilla
• Civ V
• Spiral Knights
• KOTOR
• TF2
• Thief
• Total War Shogun 2
• Tropico 3
• Uplink
• Warhammer 40k
• I regret alot of things.

list is doing weird things to my post...idk

• Amnesia: The Dark Descent
  
• Aquaria
• Battlefield 2
  
• Bionic Commando Rearmed
  
• Bioshock
• Borderlands
• Braid
• Counter Strike Source
• Crysis Warhead
• Dark Void Zero
• Deus Ex Game of The Year Edition
• Deus Ex Invisible War
  
• Devil May Cry 4
• Dragon Age Origins
• Dreamfall The Longest Journey
• The Elder Scrolls Oblivion
  
• F.E.A.R( The two DLC packs are forced downloads too, which is stupid.)
  
• F.E.A.R 2 Project Origin
• Fallout New Vegas
• Far Cry 2
  
• Garrys Mod
• Gish
  
• Half Life 2 ( And Episode 1 & 2)
• Hitman 2
• Hitman Blood Money
• Hitman Codename 47
• Just Cause 2
  
• Left 4 Dead
• Left 4 Dead 2
  
• The Longest Journey
  
• Lugaru HD
• Machinarium
• Magicka
• Metro 2033
• Monday Night Combat
• Monkey Island 2
  
• Mount and Blade Warband
• Mount and Blade With Fire and Sword
  
• Oddworld : Strangers Wrath
• Operation Flashpoint Dragon Rising
• Osmos
• Penumbra Overture
• Portal
  
• Prince of Persia (2008)
• Prince of Persia The Sands of Time
  
• Prince of Persia Warrior Within
• Prince of Persia The Two Thrones
• Prince of Persia The Forgotten Sands
• Puzzle Agent
  
• Red Faction Guerrilla
• Red Orchestra ( Yay for Part 2 )
  
• Revenge of The Titans
• S.T.A.L.K.E.R Call of Pripyat
•  S.T.A.L.K.E.R Shadow of Chernobyl
  
• The Secret of Monkey Island
• Civ IV
  
• The Sims 3
  
• Tales of Monkey Island (Episodes 1 & 2 only)
  
• Team Fortress 2
• Terraria
• Thief Deadly Shadows
• Splinter Cell
  
• Splinter Cell Chaos Theory
  
• Splinter Cell Double Agent
  
• Splinter Cell Conviction
  
• Torchlight
  
• Trine
  
• The Witcher 2
  
• World of Goo
  

• Max Payne
• Max Payne 2
  
• Grand  Theft Auto IV (And the DLC)
  
• Grand Theft Auto 3 ( Still awesome)
  
• The Saboteur (This game is so much damned fun!)
  
• Baldurs Gate 1 & 2 ( The TUTU mod as well)
  
• Arcanum
  
• Descent 1 & 2
• One Unit Whole Blood
• The Witcher Enhanced Edition
  

Just 42 games for me.

• Alien Swarm
• Audiosurf
• Battlefield 2
• Battlefield: Bad Company 2
• Bejeweled 3
• Bioshock
• Borderlands
• Brothers in Arms: Hell's Highway
• Call of Duty: Modern Warfare 2
• Counter-Strike: Source
• Cryostasis
• Crysis
• Death to Spies
• Death to Spies: Moment of Truth
• Deus Ex: Game of the Year Edition
• The Elder Scrolls IV: Oblivion
• Frozen Synapse
• Garry's Mod
• Grand Theft Auto IV
• Grand Theft Auto: Episodes from Liberty City
• Grand Theft Auto: San Andreas
• Grand Theft Auto: Vice City
• Half-Life 2
• Half-Life 2: Episode Two
• Hitman: Blood Money
• Just Cause 2
• Metro 2033
• Mount & Blade: Warband
• No One Lives Forever 2: A Spy in H.A.R.M.'s Way
• On the Rain-Slick Precipice of Darkness, Episode One
• Puzzle Quest 2
• Red Faction: Guerrilla
• S.T.A.L.K.E.R.: Call of Pripyat
• S.T.A.L.K.E.R.: Clear Sky
• Team Fortress 2
• Thief: Deadly Shadows
• Tom Clancy's Splinter Cell: Chaos Theory
• Torchlight
• Unreal Tournament
• Vampire: The Masquerade - Bloodlines
• The Witcher: Enhanced Edition - Director's Cut
• XIII

But there's another 33 that are not installed in my Steam list...

I added the original Dungeon Siege, and its expansion Legends of Aranna. 
 
Also added, Mini Ninjas. Both games were very cheap so thought why not?
 
Next on the list has to be Witcher 2: only worried I won't be able to run it. Don't want to wait for an inferior XBox version.

Not that many games at the moment.
 
Battlefield Bad Company 2
Counter-Strike Source   
Crysis 2
Dead Space 2
F.E.A.R. 3
Left 4 Dead 2 
Minecraft
World of Warcraft

-World of Warcraft  (inactive account, might activate sometime) 
-Starcraft 2 
-Crysis 2 
-Fallout New Vegas 
-Unreal Tournament 2004 
-Borderlands (Have beat this game to hell and back, at least 7 different times) 
-Diablo 2 LoD (Also beaten to hell and back, Total in game play time: ~2months?) 
-Stalker: Call of Pripyat 
-Dungeon Siege 2 (Hate this game, will probably uninstall) 
-Team Fortress 2 
-Battlefield Badcompany 2
-Spiral Knights 
-Alliance of Valiant Arms 
-Various Emulators and Flash Games 
-Bulletstorm 
-All Points Bulletin
---Ghooble

Let's see
 Steam:
Altitute
Aquaria
Audiosurf
Beat Hazard
Bit trip bit
bit trip runner
Braid
Breath of Death VII
Company of heroes
Company of heroes opposing fronts
Counter Strike Source
Cthulhu saves the world
Dark void zero
Defense grid
DIRT 2
Dungeons of Dredmor
Guild Wars 
Half Life 2 ep 1
Jamestown
King's bounty: The Legend
L4D2
Machinarium
Magicka 
Penny arcade ep1 and 2
Poker Night at the Inventory
Portal
Recettear
Rhythm Zone
Sam and Max 103
Samorost 2
Civ 4
Super Meat Boy
Tales of Monkey Island ep 1
Team Fotress 2
Time Gentlemen, PLease!
Toki Tori
Trine
Witcher 2
World of Goo
 
Non Steam:
Baldur's Gate 2
Bejeweled Blitz
Star Craft 2
Civ 5
Planescape Torment
Divine Divinity 
Ass Creed 2
Dead Space 2
League of Legend
Blaz Blue
The Spirit Engine 2
Elona
tohou project games
countless free japanese shmups
 
Damn, I think I have a problem lol. And the worst thing is I don't even really have time to play games with working full time and all. I just kinda like having all of the options.

Have about 40 games installed. Can't be bothered to list them all.

Team Fortress 2 
Puzzle Agent 
Super Meat Boy 
Vampire The Masquerade Bloodlines 
Machinarium 
Braid 
Age of Conan 
Call of Duty 4 
KOTOR 

Alice: Madness Returns
Alien Swarm
Battlefield: Bad Company 2
Call of Duty Black Ops
Counter-Strike: Source
Day of Defeat: Source
Guild Wars
Lead & Gold
Left 4 Dead
Left 4 Dead 2
Portal 2
Red Orchestra
Team Fortress 2
Total War: Shogun 2
Warcraft III: Frozen Throne
Warhammer 40K Dawn of War II: Retribution

• Alien Breed 2: Assault
  
• Amnesia: The Dark Descent
• Audiosurf
• Battlefield 2
  
• Borderlands
• Clive Barker's Jericho
• Counter-Strike
• Counter Strike: Condition Zero
• Counter-Strike: Condition Zero Deleted Scenes
• Counter-Strike: Source
• Day of Defeat: Source
• DOOM 3
• Fallout
• Fallout 2
  
• Half-Life 2
• Half-Life 2: Episode 1
• Half-Life 2: Episode 2
• Half-Life: Source
• Left 4 Dead 2
• Mass Effect
• Max Payne 2: The Fall of Max Payne
• The Misadventures of P.B. Winterbottom
• NyxQuest
• Painkiller: Black Edition
• Penumbra: Overture
• Portal
• S.T.A.L.K.E.R. Shadow of Chernobyl
  
• S.T.A.L.K.E.R. Clear Sky
• Super Meat Boy
• Team Fortress 2
• Tomb Raider: Anniversary

I have 59 games.

Tada. 
 
 

Plants VS Zombies, all you need dawg.

to many to list

I sadly don't have too many games installed, as I mostly play free browser games ( The Settlers Online, SoccerStar and other such kinda crappy games.) Otherwise I have:
- BF2
- Diablo II
- Blitz1941
- Runes of Magic
- Lord of the Rings Online 
- Super Hero Squad Online

I just added Dawn of War: Dark Crusade and Soulstorm to my collection. Really rapt with these 2, and I am actually having more fun playing these than Starcraft 2! Not saying SC2 is bad, just enjoying Dawn of War more.
 
Also FINALLY installed The Orange Box... a few years too late, but still damn good.
 
Been playing more PC games than console lately!

On my desktop: all of them. 
 
On this Macbook Running Windows Vista: 
Dungeon Seige 
Warcraft 3 
The Sims 3  
Dragon Age 
Psychonauts 
Recettear 
Torchlight

Ok,  
 
Baldur's Gate 2 
Dragonsphere 
Civ 4 + Expansions 
Torchlight 
Tyrian 2000 
 
 
That's about it.

Lets see here...  Open up my games folder.. holy crap I have way to many. Alright here we go. 
Sam and Max the Devil's Playhouse 
Tales of Monkey Island  
Secret of Monkey island Special Edition 
Monkey Island 2 Special Edition 
Puzzle Agent 1 & 2 
Battlefield bad Company 2 
Just Cause 2 
Unreal Tournament 2004 
Unreal Tournament 3 
Starcraft 2 
Braid 
GTA 4 + Episodes of Liberty City 
Warcraft 3 + Frozen Throne 
Torchlight 
Crysis + Crysis Warhead 
Crysis 2 
Super Street Fighter 4 Arcade Edition 
Half-life 2 + episode 1, 2 and Deathmatch 
Half-life 1 
Team Fortress 2 
Rift 
Jamestown 
Mass Effect 1 
Mass Effect 2 
Leagues of Legends (I actually never played it) 
Minecraft 
Magic the Gathering : Duels of the Planeswalker 2012
Portal 
Portal 2 
Poker night at the inventory 
Super Meatboy 
Counter-Strike Source 
Call of Duty : Modern Warfare 2 
Left 4 Dead 
Left 4 Dead 2 
Dragon Age Origins 
Dragon Age 2 
Elder's Scroll Oblivion 
Civilzation 4 
HAWX 2 
The Witcher 
The Witcher 2 
Trine 
Need For Speed : Hot Pursuit 
Garry's mod 
World of Warcraft.
 
Yay for Steam Sales 
 
I never uninstall my games, good thing I have a 1 TB drive just for games and that hard drives are so cheap these days.

@JusticeJanitor - I just got a 500GB disk exactly for that purpose :)

Mass Effect 2

Dragon Age 2

Knight of the Old Republic

The Witcher 2

Fallout: New Vegas

Civ 5

Left 4 Dead 2

Portal

Portal 2

Bioshock 2

Dead Space 2

Super Meat Boy

Need for Speed: Hot Pursuit

The Longest Journey

Dreamfall

Let's see...
 
Amnesia: Dark Descent
Borderlands

HL2 
L4D2
Portal
Portal 2
Super Meat Boy
TF2
Torchlight
Trackmania United (Ooh I should boot this up)
AaAaAA!!! A Reckless Disregard for Gravity
Alien Breed 2 Assault
Beat Hazard
The Cat and the Coup
Company of Heroes
Garry's Mod
Gratuitous Space Battles
Guild Wars Trilogy
Hamilton's Great Adventure
Hitman: Blood Money
Hydrophobia: Prophecy
Ion Assault
Killing Floor
Kings Bounty: Armored Princess and Crossworlds
Lead and Gold Games of the Wild West
Magic the Gathering 2012
Metro 2033
Mount and Blade Warband
Naval Warfare (just bought this because it was 2.50 and it looks kinda cool.)
Neverwinter Nights 2 Platinum
RUSH
Sanctum
Spiral Knights
Swarm Arena
Terraria
VVVVVV 
The Wonderful End of the World
 
So that's just Steam
 
Now scattered about retail releases:
Resident Evil 5
Arkham Asylum
Witcher 1
Bejeweled 3
Saira (well not Steam anyway)
 
And to top it off, how about a little X Blades. Yeah I bought that fucking stupid ass broken game. I had forgotten it until now.