here is a nice build, hope it helps you.
PCPartPicker part list:
http://pcpartpicker.com/p/vHUo
Price breakdown by merchant: http://pcpartpicker.com/p/vHUo/by_merchant/
Benchmarks: http://pcpartpicker.com/p/vHUo/benchmarks/
CPU: Intel Core i5-3470 3.2GHz Quad-Core Processor ($179.99 @ Amazon)
Motherboard: ASRock H77 Pro4/MVP ATX LGA1155 Motherboard ($87.55 @ Newegg)
Storage: Western Digital Caviar Blue 500GB 3.5" 7200RPM Internal Hard Drive ($57.99 @ Amazon)
Video Card: MSI Radeon HD 7850 2GB Video Card ($179.99 @ Amazon)
Case: Cooler Master HAF 912 ATX Mid Tower Case ($59.99 @ Amazon)
Power Supply: Corsair Builder 600W 80 PLUS Bronze Certified ATX12V Power Supply ($66.24 @ Amazon)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer ($16.99 @ Newegg)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) ($92.65 @ Amazon)
Total: $741.39