Video Games

Use PartPicker.
This is a breakdown of the kind of build that I'm considering - ( I already have a 1TB hdd and I would buy 8gb DDR3 1600mhz memory from CEX for £30). I must admit that I'm may leave out the SSD drive as it's not essential.

PCPartPicker part list: http://uk.pcpartpicker.com/p/2c7v2
Price breakdown by merchant: http://uk.pcpartpicker.com/p/2c7v2/by_merchant/
Benchmarks: http://uk.pcpartpicker.com/p/2c7v2/benchmarks/

CPU: AMD FX-6300 3.5GHz 6-Core Processor (£83.99 @ Aria PC)
Motherboard: Gigabyte GA-78LMT-USB3 Micro ATX AM3+ Motherboard (£37.57 @ Aria PC)
Storage: Kingston SSDNow V300 Series 120GB 2.5" Solid State Disk (£59.99 @ Aria PC)
Storage: Western Digital RE3 1TB 3.5" 7200RPM Internal Hard Drive (£37.00 @ Amazon UK)
Video Card: XFX Radeon HD 7850 2GB Video Card (£113.99 @ Aria PC)
Case: Fractal Design Core 1000 USB 3.0 MicroATX Mid Tower Case (£29.99 @ Ebuyer)
Power Supply: Corsair CX 430W 80+ Bronze Certified Semi-Modular ATX Power Supply (£37.27 @ Amazon UK)
Total: £399.80
(Prices include shipping, taxes, and discounts when available.)
(Generated by PCPartPicker 2013-11-30 19:44 GMT+0000)

430w psu isn't big enough imo, it will be ok for a bit but you should use a slightly bigger psu to allow for how they loose a bit over time.

Ram/SSDs from cex they buy in bulk of refurbs if they are in new boxes or they are sold in by people(often as they are failing). I know a few people who have sold hdds and gpus that had been on the blink or cooked them up to "reflow" the chips to work just for the quick(if any) shop testing.

Would avoid aria too as they have bad returns/refunds/packing. Have had stuff in the past arrive with the boxes all trashed and the stuff inside almost broken as they are too cheap to use packing so just put things in jiffy bags and let it get bashed to bits. Check scan, cclonline and overclockers or even order from caseking in germany(they own overlockers).

MSI 7850 on overclockers for £90.