I'm too lazy to look anything up for myself on the internets, so I'll get some of you suckers to do it for me.
Radeon HD 2900 pro - £150
Nvida 8800 gts 320mb - £160
Nvida 8800 gts 640mb - £200
Which is the most 'sensible' one of the three to buy, is the memory increase on the 640mb 8800 worth it?
Any other suggestions are good, I know what you nubs are like.