By far the best value for money at the moment is the 6600GT. If you go for one with 256MB video ram (for those games with hooj textures like quake...), it performs better than a stock 6800 with 128 MB...
it's also worth looking for a good brand as well - like Leadtek, BFG, XFX.... - because not all 6600GTs are made the same and the few extra pounds are worth it.
Incidentally, it's getting harder and harder to find anywhere with the better cards in stock - they're all moving on to pci-e
:-D
