Here is a build i put together, included windows 7 but no keyboard/mouse
PCPartPicker part list:
http://pcpartpicker.com/p/1ycnt
Price breakdown by merchant: http://pcpartpicker.com/p/1ycnt/by_merchant/
Benchmarks: http://pcpartpicker.com/p/1ycnt/benchmarks/
CPU: AMD FX-6300 3.5GHz 6-Core Processor ($109.99 @ Amazon)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler ($29.99 @ Microcenter)
Motherboard: Asus M5A97 R2.0 ATX AM3+ Motherboard ($93.98 @ Outlet PC)
Memory: Corsair Vengeance 8GB (2 x 4GB) DDR3-1866 Memory ($72.90 @ Newegg)
Storage: Western Digital Caviar Blue 500GB 3.5" 7200RPM Internal Hard Drive ($54.98 @ Outlet PC)
Video Card: Sapphire Radeon HD 7870 GHz Edition 2GB Video Card ($175.66 @ Newegg)
Case: Corsair Carbide Series 300R Windowed ATX Mid Tower Case ($65.99 @ NCIX US)
Power Supply: Corsair Enthusiast 650W 80 PLUS Certified ATX12V / EPS12V Power Supply ($69.99 @ Newegg)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer ($16.98 @ Outlet PC)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) ($89.98 @ Outlet PC)
Total: $780.44
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-08-30 23:33 EDT-0400)