Uncharted as that's cheap TPS, then Uncharted 2 later when the price comes down (since you seem the patient type) although replay may be limited unless you go after Platinum Trophy
Oblivion GOTY edition has all the DLC I believe (or all the big stuff anyway) if you want to play it on PS3 - lots of value in this bad boy
LittleBigPlanet can be got cheap and is good and replay is endless with lots of new levels still being published today.
Ratchet and Clank Tools of Destruction is guns/platform/TPS and cheap currently plus lots of replay
You might like Folklore (I did) which is cheap action 'lite' RPG
VC I'd recommend too. Not sure how cheap it is now.
If you like Wipeout type games then get Wipeout HD & Fury expansion for sure.
Try to be reasonable... its easier than you think...
