Uncharted: Drake's Fortune is pretty good, you can get it used for like $25 I bet.
Assassin's Creed is priced new now at $30 and is a good value for that price. Burnout Paradise is also $30 and looks fun, judging from the demo.

I have played CoD5 on the PC, it is ok if you're a fan of the series, but wait until you can buy it used for like $25-30. The single player campaign is fun but not as good as CoD4, and the multiplayer is just all right.

I've also got Guitar Hero: World Tour and play it pretty much every day. If you're a fan of the plastic instrument rhythm games, I highly recommend it.