PCPartPicker part list:
http://pcpartpicker.com/p/3flEc
Price breakdown by merchant: http://pcpartpicker.com/p/3flEc/by_merchant/
Benchmarks: http://pcpartpicker.com/p/3flEc/benchmarks/
CPU: AMD Athlon X4 750K 3.4GHz Quad-Core Processor ($79.98 @ OutletPC)
Motherboard: MSI FM2-A75MA-E35 Micro ATX FM2 Motherboard ($57.78 @ Newegg)
Memory: G.Skill Ripjaws X Series 4GB (2 x 2GB) DDR3-1600 Memory ($45.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($57.98 @ OutletPC)
Video Card: EVGA GeForce GTX 750 1GB Video Card ($118.99 @ NCIX US)
Case: Antec One ATX Mid Tower Case ($34.99 @ NCIX US)
Power Supply: Corsair Builder 430W 80+ Bronze Certified ATX Power Supply ($19.99 @ Micro Center)
Optical Drive: Asus DRW-24B1ST/BLK/B/AS DVD/CD Writer ($19.98 @ OutletPC)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) ($84.98 @ OutletPC)
Total: $520.66
If you can save some more money, you'll want to get 8gb of RAM. As it currently is, this computer should be able to run most games 1080p at medium settings.