Lengthy/replayable offline PC games?

I'm going to be traveling to some remote places for work and I'm looking to bring some lengthy/replayable PC games to entertain myself.  I'm running Windows on my old 2007 Macbook Pro with limited disk space.  Does anyone have any recommendations?  I already have Dragon Age, Civ 5, Super Meat Boy, Planescape Torment, and Baldur's Gate 2.  
 
Any other deep, meaty games that doesn't take a lot of disk space?

Hitman blood money, oblivion

Morrowind will keep you entertained for a good while, even the vanilla modless experience is a worthy lengthy game, and it takes about 1 GB.
 
Mount & blade : Warband is also a very good choice, I have played that game for longer then I care to admit, the native experience alone, without any mods already have at least 150hours logged, and it's under 1 GB, besides when you're done with that there are a whole bunch of great mods to try out, my personal recommendation is the Prophecy of Pendor mod, it's pretty much professional quality.

Off the top of my head:
The Witcher, ES 3 & 4 (Morrowind and Oblivion), all the Fallout games (old and new), Recettear, Torchlight, Titan Quest, the Blizzard games (Warcrafts, Starcrafts and Diablos), Total War games, Deus Ex (first one), Arcanum.

How long are you traveling? Just stick with BG2 and Planescape... and explore everything they have to offer. The richness of the stories and the depth of the games should satisfy you just fine. Forget everything else anyone recommends in this post henceforward. :)

Thanks for the great suggestions guys! (Keep them coming!)

@Ghostin: I guess I'm leaning towards the RPGs/Turn-based just because they tend to be deeper/longer games, but I'm open to virtually anything.

I'm also thinking of making a disc image of my old PS1 Final Fantasy Tactics disc and playing it on an emulator. I bought the game but never got around to trying it.

@pureguava: I think Planescape/BG2 should definitely occupy a lot of my time, but I just wanted to see what other suggestions people have. =)

All Bethesda titles (Morrowind, Oblivion, Fallout 3 -- Fallout: New Vegas, as well), Titan Quest, Divinity 2: Dragon Knight Saga (on sale on Steam ATM), The Witcher, The Witcher 2.

Mount & Blade for sure.

Some really great games mentioned already. I was going to mention Elder Scrolls 3 & 4, Neverwinter Nights, The Witcher 1 & 2, etc

Final Fantasy Tactics from the Ps1 will take you ages to get through. I recommend that a billion times

If you're into TBS strategy games Total War: Shogun 2 might be a nice investment. Master of Orion 2 is of course a classic in the genre that takes up way less space.

Despite it's not-quite-a-game status Minecraft sounds like it might be a good idea for this situation

Fallout and Fallout 2

SWAT 4.

@HitmanAgent47 said:

Hitman blood money

Winner, winner, chicken dinner.

@chw: I'd say those games you've already got will keep you entertained for a looong time.

The Witcher 1,2. Oblivion, Fallout 3 GOTY, Borderlands. 

@Danteveli said:

Fallout and Fallout 2

Beat me to it.

Borderlands GotY, The Witcher, The Witcher 2, Diablo 2, Mass Effect, Mass Effect 2. Ummm that's all I can think of at the moment. Was going to say Baldur's Gate but I see you have that covered already.

Warcraft III, both Reign of  Chaos and the expansion are great fun.

Dude, Baldurs Gate 2 :D

Borderlands GotY, Torchlight, Oblivion all come to mind..Rise of Nations too.

Torchlight is fucking awesome. Low spec requirements as well, check it out!

San Andreas, maybe?

Diablo 2 
Rollercoaster Tycoon (any of them)

  Dark Omen