First off, Let me start by saying that I don't buy my games, I rent them. That being said, Here are some of the games that I enjoyed:
American Wasteland (Sure, you probably played this alreay, But it is fun online, Especially with all of the glitches in it!
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Condemned: Criminal Origins (A very good game, If sega made more games like this they may have been doing better)
Dead Rising (I rented this for 4 months, Beat it 5 times, And got every avhievement from it, It's that good!
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GUN (You may have already played this, But even if you have rent it and play through it again, It has very easy achievements and is the most ejoyable western game that I know of, Not that there are many western games)
Saint's Row (While the single player mode isn't all that great, It has decent online play and you can customize your character wich I am always for)
Also, While I haven't played it yet, I can't wait to play crackdown.
(I know that gears of war and oblivion are not on my list. That is because I have not played them yet)