Here's my choice, the CPU should be enough, CPU is rarely the bottleneck for games these days, and it leaves us with more money for the GPU. The Barracuda serie is also a little bit faster than the WD Caviar Blue.
CPU: AMD Athlon II X4 750K 3.4GHz Quad-Core Processor ($79.99 @ Amazon)
Motherboard: MSI FM2-A55M-E33 Micro ATX FM2 Motherboard ($48.98 @ Outlet PC)
Memory: GeIL EVO Veloce Series 8GB (2 x 4GB) DDR3-1600 Memory ($53.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($59.99 @ NCIX US)
Video Card: Gigabyte Radeon HD 7850 2GB Video Card ($179.99 @ Amazon)
Case: Silverstone PS08B (Black) MicroATX Mid Tower Case ($29.99 @ Amazon)
Power Supply: XFX 550W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply ($29.99 @ Newegg)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer ($14.99 @ Newegg)
Total: $497.91
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-08-12 16:33 EDT-0400)