Ratchet, Demon's Souls , Borderlands, L4D2..Only have enough $$ to buy One.

[Cross-X]

I'd personally pick Ratchet and Clank: A Crack In Time and I recommend it to you. It'll be an awesome game and won't be disatisfied with what Insomniac has to offer with R&C.

But as a second option, Left 4 Dead 2 is a good choice as well.