the 3850 is the best readily available AGP card out there
http://www.newegg.com/Product/Prod [...] 6814102730 you can check out the review done on this site, you may need to OC to unlock its full potential though.
hunter is right, 3850 is the best, but bear in mind the extra power required to run it, make sure your PSU is up to it if you do get it!
Just put a 3850 agp into a SKT 939 board for a cheap pc for my brother (Athlon 3200+) and it does the trick indeed in the games we play, (LOTRO, NFS, COD, C&C, Prey, Stalker, hell even runs crysis) at 1280x1024 on med settings to flat out 4aa 16as full settings in LOTRO
Good build considering everything else was free and five years old
Does have its limits though and as games evolve it is ruled out of the equation but a good reason to dust of old game collections at thier best and second hand older (2004-2007) games are brilliantly cheap, play the games you always wanted but never got around to buying or could afford to by!
What cpu do you got? If you can buy a new PCIe motherboard for a 70$, I would strongly suggest you to do that. Most of the agp card cost more than twice the price of their pcie counterparts.