Are you building it yourself? If you are, here are some part i suggest. Includes windows 7 in there, plus a 180GB ssd which is enough to store your OS, games and programs. The 7870 can run any game on high-max settings. Very nice, soundproofed case and quality and reliable PSU. There is overclocking potential due to the k edition core and 212 evo cooler. The z77 extreme4 is an excellent motherboard and has great overclocking tools and potential.
PCPartPicker part list:
http://pcpartpicker.com/uk/p/uUlf
Price breakdown by merchant: http://pcpartpicker.com/uk/p/uUlf/by_merchant/
Benchmarks: http://pcpartpicker.com/uk/p/uUlf/benchmarks/
CPU: Intel Core i5-3570K 3.4GHz Quad-Core Processor (£161.99 @ Aria PC)
CPU Cooler: Cooler Master Hyper 212 EVO 82.9 CFM Sleeve Bearing CPU Cooler (£25.45 @ Scan.co.uk)
Motherboard: ASRock Z77 Extreme4 ATX LGA1155 Motherboard (£101.98 @ Dabs)
Memory: Mushkin Blackline 8GB (2 x 4GB) DDR3-1600 Memory (£31.57 @ Aria PC)
Storage: Seagate Barracuda 1TB 3.5" 7200RPM Internal Hard Drive (£52.20 @ Aria PC)
Storage: Intel 330 Series 180GB 2.5" Solid State Disk (£99.98 @ Novatech)
Video Card: XFX Radeon HD 7870 GHz Edition 2GB Video Card (£191.74 @ Scan.co.uk)
Case: Fractal Design Define R4 (Black Pearl) ATX Mid Tower Case (£89.29 @ Scan.co.uk)
Power Supply: SeaSonic 620W 80 PLUS Bronze Certified ATX12V / EPS12V Power Supply (£85.42 @ Amazon UK)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer (£12.98 @ Scan.co.uk)
Operating System: Microsoft Windows 7 Home Premium SP1 (OEM) (64-bit) (£69.98 @ Aria PC)
Total: £922.58
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2012-12-30 02:51 GMT+0000)