Decent gaming PC for less than $500

[SuperRafal]

PCPartPicker part list / Price breakdown by merchant

CPU: AMD Athlon X4 760K 3.8GHz Quad-Core Processor ($77.99 @ Newegg)
CPU Cooler: Zalman CNPS5X Performa CPU Cooler ($26.99 @ Newegg)
Motherboard: MSI A78M-E45 Micro ATX FM2+ Motherboard ($47.99 @ Newegg)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1866 Memory ($56.99 @ Newegg)
Storage: Western Digital Caviar Blue 1TB 3.5" 7200RPM Internal Hard Drive ($49.99 @ Newegg)
Video Card: PowerColor Radeon R9 280 3GB TurboDuo Video Card ($159.99 @ Newegg)
Case: Antec VSK-3000 MicroATX Mid Tower Case ($24.99 @ Newegg)
Power Supply: Corsair CX 600W 80+ Bronze Certified Semi-Modular ATX Power Supply ($53.99 @ Newegg)
Total: $484.92
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2014-11-27 02:08 EST-0500

All parts from newegg. Switching vendors is not appriciated.

 

[i7Baby]

Try -

CPU: AMD FX-6300 3.5GHz 6-Core Processor ($89.99 @ Newegg)
Motherboard: Gigabyte GA-970A-D3P ATX AM3+/AM3 Motherboard ($62.00 @ Newegg)
Memory: G.Skill Ares Series 8GB (2 x 4GB) DDR3-1600 Memory ($78.99 @ Newegg)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive ($49.99 @ Newegg)
Video Card: MSI Radeon R9 270X 2GB TWIN FROZR Video Card ($139.99 @ Newegg)
Case: Corsair 300R ATX Mid Tower Case ($79.99 @ Newegg)
Power Supply: XFX 550W 80+ Bronze Certified ATX Power Supply ($52.99 @ Newegg)
Total: $553.94 (its $30 more expensive at Newegg)