This would be a good spec for gaming, for your budget.
Case
COOLERMASTER HAF 912 PLUS MID TOWER GAMING CASE
Processor (CPU)
AMD PHENOM II X4 970 (3.50GHz/8MB CACHE/AM3) - BLACK EDITION
Motherboard
ASUS® M5A87: AM3+ PLATFORM, DUAL DDR3,SATA 6.0GB/s, USB 3.0
Memory (RAM)
8GB SAMSUNG DDR3 DUAL-DDR3 1333MHz (2 X 4GB) - You can reduce the ram to 4gb as 4gb should still be enough just for gaming.
Graphics Card
2GB AMD RADEON™ HD6970 - 2 DVI,HDMI,2 mDP - DX® 11, Eyefinity 4 Capable
Memory - 1st Hard Disk
750GB WD CAVIAR BLACK WD7502AAEX, SATA 6 Gb/s, 64MB CACHE (7200rpm)
1st DVD/BLU-RAY Drive
24x DUAL LAYER DVD WRITER ±R/±RW/RAM
Power Supply
CORSAIR 650W ENTHUSIAST SERIES™ TX650 V2-80 PLUS® BRONZE (£72)
Processor Cooling
STANDARD AMD CPU COOLER
Sound Card
ONBOARD 8 CHANNEL (7.1) HIGH DEF AUDIO (AS STANDARD)
Network Facilities
ONBOARD 10/100/1000 GIGABIT LAN PORT - AS STANDARD ON ALL PCs
USB Options
6 x USB 2.0 PORTS @ BACK PANEL (MIN 2 FRONT PORTS) AS STANDARD
Operating System
Genuine Windows 7 Home Premium 64 Bit - inc DVD & Licence (£79)
Office Software
NO OFFICE SOFTWARE
Anti-Virus
NO ANTI-VIRUS SOFTWARE
Warranty
3 Year Silver Warranty (1 Year Collect & Return, 1 Year Parts, 3 Year Labour) (£5)
Delivery
STANDARD INSURED DELIVERY TO UK MAINLAND (MON-FRI)
Build Time
Standard Build - Approximately 10 to 12 working days
Quantity
1