Budget Computer for Gaming and Editing

I didn't include an OS or a monitor, which you may already have. You could swap the Silverstone 600w for a Rosewill 530 and get down to $610

Part list permalink / Part price breakdown by merchant

CPU: Intel Core i5-2500K 3.3GHz Quad-Core Processor ($179.99 @ Microcenter)
CPU Cooler: Cooler Master Hyper 212 Plus 76.8 CFM Sleeve Bearing CPU Cooler ($19.99 @ Newegg)
Motherboard: Gigabyte GA-Z68MA-D2H-B3 Micro ATX LGA1155 Motherboard ($95.99 @ NCIX US)
Memory: G.Skill Value Series 8GB (2 x 4GB) DDR3-1333 Memory ($37.99 @ Newegg)
Hard Drive: Western Digital Caviar Blue 250GB 3.5" 7200RPM Internal Hard Drive ($69.70 @ NCIX US)
Video Card: PowerColor Radeon HD 6790 1GB Video Card ($104.99 @ Newegg)
Case: Apex Vortex 3620 ATX Mid Tower Case ($34.99 @ NCIX US)
Power Supply: Silverstone 600W ATX12V / EPS12V Power Supply ($68.98 @ NCIX US)
Optical Drive: LG GH24NS70 OEM DVD/CD Writer ($17.98 @ Newegg)
Total: $630.60
(Prices include shipping and discounts when available.)
(Generated 2012-04-01 15:23 EDT-0400)