Ok, with that power supply you cant go into the Geforce 200 series as most of them require a 500W power supply, so it would limit you to maybe the 9800 series. If you were looking at ATI's cards, then there isnt really a limit as all cards above 450W are out of your price range.
So in my opinion you could get a :
EVGA GeForce 9800 GTX (512MB GDDR3, PCI Express 2.0, SLI Ready, (Dual Link) Dual DVI, HDTV)
You could get this card for $150