The best card out now in PCI is the v3-2000. THey will be also putting out the v3-3500 in PCI version also, but it will cost tons.
FOr lower end CPU's the V3-2000 is the best choice. You might want to read the reveiws over at anand's because he has the lower end PC's compared with different video cards. THe bottom line is a v3-2000 for anything under a p2-300-350. Above that and it becomes a harder question to answer.
Soyo sy6ba+iv Intel p3-700e@933 512meg-Cas2-2-2/
ATI Radeon 64meg DDR-vivo-/Memorex 48x//
Iomega 12x4x32x Burn Proof//