Well right now it's pretty much the new releases, Gears 3, MW3, and Halo CE Anniversary. Unfortunately, the only one of the three I actually own is Gears 3, so I can't play them on a daily basis. Darn.
I don't care if people say this isn't a 'real' game, but I प्यार Mario Kart. I'm not really into that whole Call of Duty types of games, although सड़क, स्ट्रीट Fighter II and Mortal Kombat II are some of the greatest games ever.