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 l’amour Mario Kart. I'm not really into that whole Call of Duty types of games, although rue Fighter II and Mortal Kombat II are some of the greatest games ever.