I've asked the same question in the folding forum, but here's the question posed to gamers
I'm planning on spending about £40 on the GPU for my new office, casual gaming (at 1280x1024) and folding computer. As far as I can tell my basic choice at that price is a HD4650 or a DDR2 9500GT. I've hunted around and found one direct comparison review which puts the 4650 slightly - but only *very* slightly - ahead in gaming terms: however I understand the NVidia architecture is better for folding. Adding complexity, microdirect are currently doing a clearance 8600GT 256MB for £35 which looks quite tempting.
Another (minor) consideration is that I do have an SLI capable motherboard, so I could add a second card at a later date for mutli-gpu goodness
So, any opinions, and have I missed any contenders in that price range (I can probably go a few quid over £40, but not too much).