Steam Store Game Suggestions?

Hey folks! Was just curious, but I use Steam alot and have a little bit of a collection on my Game List but I want to eventually add some more titles with GOOD REPLAY value so I was seeing what you guys think if you're a Steam user. This is the list of what I own already:
 
1.) Counter-Strike: Source
2.) Enemy Territory: Quake Wars
3.) Left 4 Dead
4.) Day of Defeat: Source
5.) Team Fortress 2
6.) Call of Duty 4
7.) Half-Life 2 and Half Life 2: Ep1 & 2
8.) Dawn of War Gold (with expansions)
9.) Portal  
 10.) Mass Effect

Plants VS Zombies

I would definitely recommend Plants VS Zombies.  Also Dawn of War 2 is awesome but it is not anything like other RTSs.  The Witcher is also an amazing RPG/game where you try and have sex with as many women as possible.

Peggle.
World in Conflict.
BioShock.

If you want Half-Life 2 (episodes included) and team Fortress 2, you might as well buy the Orange Box.  You can also buy Counter-Strike Source in stores that includes Day of Defeat Source if you want either of those.

Knights of the Old Republic is on steam. get it if you don't have it.

The id super pack :)

Id reccomend the freedom force games and PvZ :)

Plants vs Zombies- Very solid value for 10 bucks
Defense Grid- Very good Tower Defense game that was recently dropped down to 10 dollars
Killing Floor- If you're looking for a different take on the Zombie Coop than L4D it can provide a lot of value for 20 bucks
Audiosurf- If you like music this can give you a whole new way to experience it and is really only limited in re-playability by your music collection

Jedi Knight II: Jedi Outcast
Jedi Knight: Jedi Academy
Garry's Mod

" Much too expensive to play on steam. Only well-heeled individuals, or their sons and daughters, can afford to. Yes, the service is "free". You can walk in the front door of a major department store for "free", too.  Yet, once inside,  you STILL have to pay for all the expensive hardware, required upgrades, and products you wish to enjoy. "

" Much too expensive to play on steam. Only well-heeled individuals, or their sons and daughters, can afford to. Yes, the service is "free". You can walk in the front door of a major department store for "free", too.  Yet, once inside,  you STILL have to pay for all the expensive hardware, required upgrades, and products you wish to enjoy. "

" Much too expensive to play on steam. Only well-heeled individuals, or their sons and daughters, can afford to. Yes, the service is "free". You can walk in the front door of a major department store for "free", too.  Yet, once inside,  you STILL have to pay for all the expensive hardware, required upgrades, and products you wish to enjoy. "

" @HAMMERCLAW said:

" Much too expensive to play on steam. Only well-heeled individuals, or their sons and daughters, can afford to. Yes, the service is "free". You can walk in the front door of a major department store for "free", too.  Yet, once inside,  you STILL have to pay for all the expensive hardware, required upgrades, and products you wish to enjoy. "

You're right. We should all throw away our computers and consoles because it's much too expensive.  Solid choices so far. Definitely check 'em out. "

" @LordAndrew said:

" @HAMMERCLAW said:

" Much too expensive to play on steam. Only well-heeled individuals, or their sons and daughters, can afford to. Yes, the service is "free". You can walk in the front door of a major department store for "free", too.  Yet, once inside,  you STILL have to pay for all the expensive hardware, required upgrades, and products you wish to enjoy. "

You're right. We should all throw away our computers and consoles because it's much too expensive.  Solid choices so far. Definitely check 'em out. "

No, they who can afford the experience should enjoy it to their hearts content. I'm just tired of hearing how wonderfully "free" it all is. "

" Much too expensive to play on steam. Only well-heeled individuals, or their sons and daughters, can afford to. Yes, the service is "free". You can walk in the front door of a major department store for "free", too.  Yet, once inside,  you STILL have to pay for all the expensive hardware, required upgrades, and products you wish to enjoy. "