My 2 cents:
I'd definately steer you towards an "affordable" ATI AGP video card
that has tremendous bang for the buck:
HIS Hightech HX85PRF256-3VIAN Radeon X850PRO 256MB 256-bit GDDR3 VIVO
AGP 4X/8X Video Card
http://www.newegg.com/Product/Product.asp?Item=N82E16814161172
This card can be flashed with an XT/PE BIOS to open up the other four
pipelines, but going that route is not for the timid nor the faint of
heart.
Of course, if you want to go completely over-the-top, you could empty
out your bank account and go for one of these:
ATI FireGL X3-256 FireGL X3 256MB 256-bit GDDR3 AGP 4X/8X Video Card
http://www.newegg.com/Product/Product.asp?Item=N82E16814102462
Mind you, the FireGL cards aren't really optimized for gaming. I just
threw it in there for the "Huh?! Say what?!" factor.
FWIW, I just purchased the HIS card (first card listed above) as a
"last hurrah" for my aging AMD Athlon 2600+ based system and it works
exceptionally well as a replacement for the HIS Hightech 9800PRO 128MB
AGP card that was in there.
Now, there are a lot of "other" (translation: non-ATI chipset) options
for high-end AGP cards out there...but you did say ATI, right.
Hope I've been able to be of service to your cause,
Paul_in_NC