Assuming that you don't play games, and you don't need an operating system, I made a build suggestion for you:
PCPartPicker part list:
http://pcpartpicker.com/p/u7hW
Price breakdown by merchant: http://pcpartpicker.com/p/u7hW/by_merchant/
Benchmarks: http://pcpartpicker.com/p/u7hW/benchmarks/
CPU: Intel Core i5-3570 3.4GHz Quad-Core Processor ($209.99 @ SuperBiiz)
Motherboard: ASRock B75 PRO3 ATX LGA1155 Motherboard ($74.99 @ SuperBiiz)
Memory: Patriot Intel Extreme Master, Limited Ed 8GB (2 x 4GB) DDR3-1600 Memory ($31.99 @ Amazon)
Storage: Seagate Barracuda 500GB 3.5" 7200RPM Internal Hard Drive ($54.99 @ SuperBiiz)
Video Card: Gigabyte Radeon HD 6670 1GB Video Card ($56.97 @ Newegg)
Case: Raidmax Reiter ATX Mid Tower Case ($27.98 @ Newegg)
Power Supply: Corsair Builder 430W 80 PLUS Bronze Certified ATX12V Power Supply ($19.99 @ Newegg)
Optical Drive: Sony AD-7280S-0B DVD/CD Writer ($18.99 @ Newegg)
Total: $495.89
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2012-12-25 20:10 EST-0500)
You could still play games on this build, but don't expect playing all modern games on high/max settings. Also, I was about to recommend the i7, better for video editing, but due to the budget you have, I stayed with the i5 as you wanted. You might want to consider the AMD bulldozer or piledriver's 8 core CPUs, they are not good at gaming, but they are good at multi-thread programs, such as video editing, in some cases, it even outperforms the i5 CPUs on multi-thread programs.