PCPartPicker part list:
http://uk.pcpartpicker.com/p/1W101
Price breakdown by merchant: http://uk.pcpartpicker.com/p/1W101/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/1W101/benchmarks/
CPU: AMD FX-6300 3.5GHz 6-Core Processor (£82.09 @ Aria PC)
Motherboard: Gigabyte GA-78LMT-USB3 Micro ATX AM3+ Motherboard (£38.27 @ CCL Computers)
Memory: G.Skill Ripjaws X Series 8GB (2 x 4GB) DDR3-1600 Memory (£59.99 @ Novatech)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£42.98 @ Aria PC)
Video Card: MSI Radeon HD 7950 3GB Video Card (£174.95 @ Scan.co.uk)
Case: Corsair 200R ATX Mid Tower Case (£47.78 @ Ebuyer)
Power Supply: EVGA 500W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (£41.76 @ Dabs)
Optical Drive: Samsung SN-208DB/BEBET DVD/CD Writer (£10.99 @ Amazon UK)
Total: £498.81
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-11-01 20:09 GMT+0000)
You could also swap out the 7950 for a 7870 and get an aftermarket CPU cooler.
Just based off logainofhades' suggested build.