Help building a gaming pc for £500 (excluding graphics card)

[Icecream5000]

I am looking to build a gaming PC for Guild Wars 2.
My budget is roughly £500.
I currently have a graphics card: Nvidia GeForce GTX 550 ti which is brand new.
I also have a monitor, which i does not need upgrading, but if i had enough money left over i would consider it. I would also need a mouse and keyboard. I would be playing over wireless, so i guess i would need a Wireless-N adapter as well. I also have speakers.

I live in the UK, so i would have to buy from a UK website. Would anyone be able to recommend the best build (excluding graphics card) for this price?

Thanks in advance!

 

[metal orient]

from aria.co.uk:

MICROSOFT Windows Home Premium 7 SP1 64-bit EN 1pk - OEM [GFC-02050] #38272
1TB Seagate Barracuda ST1000DM003 3.5" SATA III Hard Drive #48501
550W OCZ ZS Series 80PLUS Bronze Power Supply #45457
Antec One Black Midi Tower Gaming Case #50303
8GB Exceleram Black Sark LP ERS303B (2x4GB) 1600 (PC3-12800) 240-Pin DDR3 #51651
GIGABYTE GA-Z77-D3H Intel Z77 Socket 1155 DDR3 PCI-Express Motherboard #49019
Intel Core i5-3450 3.10GHz (Ivybridge) Socket LGA1155 Processor (77W) - Retail #49752
TP-Link Wireless 150Mbps PCI Express Adapter w/ LP Bracket [TL-WN781ND] #42761

Total price: £500.08