FPS: Call of Duty 4, Half Life 2, Team Fortress 2
RTS: Dawn of War: Winter Assault, Warcraft III: Frozen Throne, Homeworld
RPG: I’d put FFVII since I did play it once on PC, but really all my RPG experience worth noting is console based
MMO: World of Warcraft, Dawn of War: Winter Assault, Call of Duty 4
Sandbox: Again, most of what I’d consider great sandbox is console based for me
Other: Day of Defeat: Source, Portal, Every Rom Game I’ve Ever Had
Obviously horribly biased and probably missing some incredible game that I’m forgetting for no good reason. That’s the only thing I hate about these lists 
EDIT: See! I forgot Bioshock. I’m ashamed of myself now.
So, new:
FPS: Bioshock, Half Life 2, Call of Duty 4
MMO: World of Warcraft, Dawn of War, Team Fortress 2