PCPartPicker part list: http://pcpartpicker.com/p/iQgN
Price breakdown by merchant: http://pcpartpicker.com/p/iQgN/by_merchant/
CPU: Intel Core i5-3570 3.4GHz Quad-Core Processor ($209.98 @ SuperBiiz)
Video Card: Gigabyte Radeon HD 7950 3GB Video Card ($297.98 @ SuperBiiz)
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-01-26 23:19 EST-0500)
Base Total: $496.98
should do the trick.