Well, it depends what you wanna do.
I can give you a free AGP GeForce 4 MX 64mb if you like.. That for instance is a good card for the person who wants their PC to do anything around Windows and maybe flirt with playing games etc. If you are gunna play the latest games, or do some 3D modelling / rendering / cgi then you're gunna need to go to the next level.
Radeon 9700 and upward.. But I hear the 9600xt is a good card and is reasonably priced - in the 200 ballpark.
Innit.