I just got it this past Christmas, so I don't have that many games, so far:
Halo Reach (My Favorite right now)
Batman: Arkham Asylum (Was my favorite but the first Scarecrow sequence scared the shit out of me - don't laugh! So I'm taking a break lol)
Motral Kombat VS DC Universe (Great graphics and hard hitting!)
Marvel Ultimate Alliance (Fun, but kinda repetetive, wanna get #2 when I get through this one)
Call of Duty: Modern Warfare 2 (Who has an Xbox and doesn't have this)
Project Gotham 3 (Sweeeet racing)
Forza Motorsports (Meh)
Midnight Club: Los Angeles (Meh)
Transformers the Game (HORRIBLE!!!! and I wouldn't get much if I trade it in so I just apply all the cheats to it - makes it a bit more managable!)
Gears of war (Great game! Haven't played it much yet though)
And a couple of the cheezy Kinect games!
And just for shits and giggles I got a few games on my pc too, (I play them with a wired Xbox controller, works great with Windows... most notably:
Bond: Bloodstone
Spiderman Web of Shadows
Spiderman Shattered Dimensions
GTA: Vice City
Some of the Leisure Suit Larry series
Assasins Creed II