i thought assassins was good the first time around. Although it is quite repetitive, so do as much as you can your first go achievement wise before you realize wtf i just did the same thing thirty times!!......Like i did :p
Halo 3 or Modern warfare...or any popular fps multiplayer that is fun on live
Fallout 3: Still working on it myself. Not as addicting as Oblivion, but maybe thats just because i realized i spent half of my fall semester playing it!
A guitar related game (rockband or GH)
and GTA4.....need i say more. Its the newest GTA, thats enough for me.