I think the fastest PCI boards are the either the Hercules 9000 PCI or the new AIW VE, based on the Radeon 7500. The Hercules board is faster than the Powercolor 9000 PCI and is priced accordingly:
Herc. card
The Herc. card is also huge, so keep that in mind if you have a small case. It is clocked at 250/400 and according to all evidence, cannot be overclocked.
Rage3D did a review of the AIW VE here:
AIW VE review
Their test pc has almost identical specs. as mine, and the numbers they posted are very impressive for a PCI card (plus you get all the extra features). It spanks the crap out of my Powercolor 9000 PCI (PC 9000 PCI's are clocked at 250/380 and also cannot be overclocked). The AIW was clocked at 260/500 (nice!) and they were able to overclock it pretty well.
NOTE: The AIW is being priced at right about $120-130 in most stores, but CompUSA currently has it for $129, with a $30 Mail in rebate, so your final price will be $99. Not too bad.
If you want to go Nvidia, then the fastest card is probably the MX440 PCI. You can find a number of vendors selling this card at Pricewatch:
link
Just search in the video card section for MX440 PCI. These cards will be a little cheaper than the Herc. 9000 PCI or the AIW VE.