Computer Games:
AirAttack (Mac App Store)
American McGee's Alice (Mac Demo, Retail PC DVD)
Amnesia: The Dark Descent (Mac App Store)
Battlefield 1942 (Retail Mac DVD)
Call of Duty (Mac App Store, Retail PC DVD)
Call of Duty 2 (Amazon Digital Download, Retail PC DVD)
Call of Duty 4 (Amazon Digital Download, Retail PC DVD)
Diablo III (PC+Mac Digital Download)
Doom 3 (Mac App Store)
Halo (Mac Demo, Retail PC DVD)
Lord of the Rings: Return of the King (Retail Mac DVD)
Modern Combat Domination (Mac App Store)
N.O.V.A. 2 (Mac App Store)
Portal (Steam PC+Mac)
Portal 2 (Steam PC+Mac)
Quake Live (Free Web-Based Game)
Prey (Retail Mac DVD)
Sonic Adventure DX (Retail PC DVD) nostalgic of my Dreamcast days...

)
Trine (Mac App Store)
World of WarCraft (PC+Mac Digital Download Trial, just started playing...

)
Xbox Games:
Call of Duty 3 (360)
Call of Duty: Modern Warfare 2 (360)
Call of Duty: Black Ops (360)
Gears of War 2 (360)
Grand Theft Auto III (Xbox)
Grand Theft Auto: Vice City (Xbox)
Halo 2 (Xbox)
Halo 3 (Xbox 360)
Madden '07 Hall of Fame Edition
Mass Effect 2 (came with my second Xbox 360 purchase, never understood that game...)
Namco Museum (Xbox)
Pure (360)
I'll definitely be getting more PC games in the future, as I was given a load of PC parts recently from a family friend (he was just going to throw them out) and now have a pretty capable gaming machine. At least for the games I want to play anyways...