every card performs better on a faster cpu!
It depends on what you'd use it for, and what motherboard you have. The all around and most reliable cards are the ATI chipsets.
*ATI Rage Fury Pro is a decent one,
ATI Fury Maxx if you want power,
!ATI Radeon(s) if you wanna blow away your computer
and invest in the future.
*Matrox G400 is really good for everything! It is fast, includes TV in/out, etc.
Diamond Viper TNT2 Ultra is really powerful for now.
*Diamond Viper 2 is even more powerful.
*Voodoo3 3000 is fast, nice, but only 16 bit.
Voodoo3 3500 includes a tv tuner.
*GeForce cards (azus, annihilator, etc) are not good to get now, just for investment sake...
!GeForce2 GTS cards are of the future too.
Cards with a "*" are current recomendations because your cpu may not be able to feed enough data.
Cards with a "!" are ones you'd get of you plan in upgrading to a very powerful system soon.
These are the mainline cards i'd stick with. Hope this helps out!