I will be building a budget gaming PC with my friend in around a months time.
The Specs we've gone with are:
AMD Phenom II x4 965 Black Edition (Already bought - was only £50 for one day on amazon!!)
Sapphire AMD Radeon 7770 1GB
8GB 1600Mhz Corsair Vengeance RAM
1TB WD Caviar Blue
Asus M5A97 R2.0 Motherboard
Zalman Z9 Plus Case
Corsair CX430w PSU
So we have the processor and if you have anything in the spec list you think we should change / consider other options then please let me know - be sure that it stays in the price range xD
Remember that we're from the UK so we can only get components from an UK website
Pictures of the build process will be up as soon as we get all the parts.
spend the extra £30 on a HD7850 of the extra £10-£20 on a HD7790 Asus HD7790-DC2OC-1GD5 (£114)
XFX FX-785A-ZNFC (7850 £120) - the cheapest a HD7850 has ever been here in the uk
I really like it. I think you've done well for a sub-£400 rig! I was scared that you would have an APU system put together, which don't have the best upgrade paths.
In terms of upgrades. I would try and grab the PSu below. It will be a little more in terms of cost, but this PSU ticks all the boxes. It has good voltage regulation, solid Japanese capacitors, a single 12v rail with enough amps for any single high-end GPU, bronze certified.
http://www.amazon.co.uk/ProSeries-550W-Power-Supply-Edition/dp/B004U6S1P6/ref=sr_1_3?ie=UTF8&qid=1372810144&sr=8-3&keywords=xfx+550
That will allow you to upgrade your GPU in the future, from a 7770 to something a little more powerful.
With my recommended PSU, you could pair the Phenom (very good price on that) with a 7950, if you desired.