Bump...
Okay here's some of my favorite games:
Older PC games: F.E.A.R., Pariah, Unreal Tournament 2004, Silent Hill 2 &3, AvP2, Half-Life 2, No One Lives Forever, Tron 2.0, Halo, Lost Planet, Far Cry, The longest Journey & Dreamfall, BattleZone 2, Return to Castle Wolfenstein, Doom 3, Quake 4, Giants: Citizen Kabuto, and all of the old LucasArts games from the 1990s
New PC Games: F.E.A.R. 2, Crysis, Torchlight, Time Shift, Bioshock 1& 2, Red Faction: Guerilla, Portal, Left 4 Dead 2, Mass Effect, Alien Swarm, Trine, Batman: Arkham Asylum, and I also play Modern Warfare 1 & 2. Single player for MW2 is great but multiplayer isn't since it's full of cheaters and the servers are glitchy sometimes.
Most of my newer games are on for my PS3 but I'm slowly getting them on Steam as they go on sale since I expect my PC to last a lot longer than my PS3. I've been moving over all my Steam games whenever I get a new PC and after moving it three times I haven't had any problems