The Radeon 9600Pro is a good card and is within your price range. The 9500Pro is slightly more, and harder to find, but it can be soft-modded to perform faster (more like a 9700Pro) I think. Both are DX9 compatible. If you want good graphics make the minimum a 128MB Radeon 9600Pro. I have one, and can play all games happily on 1024*786 resolution at hight graphics detail. GTA Vice City will play on 1280*1024 at high detail until it rains, but dropping the resolution to 1152*864 (can't remember specific) fixes the lag and it behaves itself, same for Freelancer and UT2003.
The Geforce FX's I don't know as much about, but Stay away from the FX5200 and I think the FX5600 should be the minimum you want. They are apparently very noisy though.
If you're upgrading make sure that the rest of your system is up to handling the faster card.
At the slighly lower end graphics, GF4 Ti4200/Ti4800 would be a decent card, but doesn't support DX9, and only if price is a problem.
I got my Saphire 128MB Radeon 9600Pro from click here been very happy with it, doesn't come with any flasy software but you won't regret it when you see it performing.
Have fun gaming.