Budget AMD Gaming Build - Need Advice

Heya folks,

Im trying to price up a new budget AMD gaming system and would be really grateful for some advice and recommendations as I tend to get carried away when pricing things up myself and blow past my budget before I realise it.

Approximate Purchase Date: Mid Feb

Budget Range: £600-900 (the lower the better)

System Usage from Most to Least Important: Gaming(MMOs and singleplayer)/Surfing/streaming programs and movies.

Parts Not Required: Speakers, OS, (would need a new mouse and keyboard)

Preferred Website(s) for Parts: Ebuyer, Aria, Scan, Amazon uk

Country of Origin: UK - England

Parts Preferences: While It is a budget system I am dead set on having it all in a NZXT Phantom Black Enthusiast Full Tower Case

Overclocking: Maybe

SLI or Crossfire: Either and maybe

Monitor Resolution: im not really sure which is best im currently using a monitor with 1280x1024

Additional Comments:
Looking at 4GB DDR 3 maybe 8 if can be got cheap enough
Also maybe a non stock cpu cooler that dosent block Dimm sockets would be nice.
Also is onboard sound better then say creative card sound?
I have a slight bias GPU wise to Nvidia cards but have used AMD/ATI ones in the past. Also I know having a monitor in the build is gonna cut what could be used for other parts but still need one.

Thanks All

Evergence