The Radeon 9000 makes a good PCI video card, but I think the best that you're going to find is a GeForce FX 5700 PCI.
I researched it rather thuroughly a while back, and ended up doing nothing on it, but I was going to get a Radeon 9000. Be careful, as many of them are AGP models that are still being sold as backstock. The 128mb version performs slightly better than the 64mb version, but not by much. If you get the 5700, go for 128mb.