Sucks that it ends on the 30th otherwise I would have said Dragon Age: Origins and Modern Warfare 2. Full price... that really doesn't leave a lot of stuff as you seem to have already played some of the best games on the system and you said you're not interested in the others I'd normally sugest. So...
inFamous- pretty fun
Star Wars: Force Unleashed- fun for a Star Wars game
Prince of Persia- cheap, but a solid platformer
Tekken 6- should be out by the deadline
Borderlands- same as above
Batman: Arkham Asylum- meant to be a great game