Simulation (real physics and courses): Gran Turismo 5. XL edition (most of the DLC and patched to 2.00) is $20. Shift is ok, but stay away from Shift 2 and ProStreet.
Arcade (NFS/Burnout/etc styled): NFS Carbon or Split/Second. each are $20. I've heard Blur is really good, but I've yet to try it, but what I've played, those two are the top (I've played all NFS games this gen, Burnout Paradise, and a few others)
PSN ID: Troll_Face_Flame (formerly armyflame) X360 gamertag: ArmyFlame9 The more people post on GameFaqs, the more I lose faith in humanity.