The 4850 is fine for the majority of games up to 1680x1050 (22" widescreen)
But don't go for that 4850, it's way too pricy, granted it's a good cooler
Instead look at the xfx £80
http://www.scan.co.uk/Products/512MB...VI-XXX-EDITION
or Sapphire Vapor-x £86 which is a very good cooler
http://www.ebuyer.com/product/161309
Or even the 4830 which is still good will easly cope with 1440x900 or 1280x1024 (17"-19")
MSI £67
http://www.ebuyer.com/product/168791
For cooler don't bother with the mini-ninja that's not a thin case, instead look ate the Akasa nero AK-967
http://www.scan.co.uk/Products/Akasa...-120mm-PWM-fan
However the Black edition AMDs come with very good stock coolers, so I not bother with an aftermarket cooler, only get one later if you're not happy with the stock cooler.
That's knocked £65-85 off the total
I'd agree with PSU, look for something else, 400-450w should be fine
I sugest
The FSP Blue storm 2, it's not the newest of psu's but it's still a good one
http://www.scan.co.uk/Products/400W-...-plus-dual-12V
Silver storm Strider, again not the newest but still good
http://www.scan.co.uk/Products/400W-...an-(22-dBA-min)
Silverpower SP-SS400 (made by seasonic), silverpower is still a new name in the psu market and they commisioned seasonic to make this good value psu
http://www.scan.co.uk/Products/400w-...2V-6Serial-ATA
For modular PSU have a look at the new Corsair 450HX
http://www.scan.co.uk/Products/450W-...-year-Warranty
Oh and always remember to check scan's today only offers before buying
That memory you listed and the corsair 450HX are both a couple of quid cheaper there atm.
Over on ebuyer again
Enermax Pro82+ 425w
http://www.ebuyer.com/product/144083
OCZ 400w StealthXStreme
http://www.ebuyer.com/product/152505
OCZ 400w ModXStreme (modular)
http://www.ebuyer.com/product/152509
EDIT: cpu, you could probably happly drop down to the 250, 245 or 240 which would save another £17-30
CAT-THE-FITH regulary recogmends the Gigabyte GA-MA770-UD3 motherboard (I think that's the one)
http://www.scan.co.uk/Products/Gigab...D3-Motherboard
Although the Gigabyte GA-MA770-
US3 would be better if you can find it as it's the same but with the better 710 south bridge