Need to know what resoultion you game at and what the make/model of your power supply is?
Depending on your PSU i'd say the best bang for your buck at $150 is the Saphire 5850.It's currently priced at TigerDirect for $160 but it's worth it.The price to performance is right on the money and it's definitly the best bang for your buck card.It's triple the performance of a 5670.
Saphire 5850 $160 + Shippinghttp://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=365434
Their is also this XFX 5850 but it's priced at $180 but it also has a $40 MIR.Just a thought if you like dealing with MIR's.
XFX 5850 $180=$140 after MIR + Shippinghttp://www.tigerdirect.com/applications/SearchTools/item-details.asp?EdpNo=6078264&CatId=3669