Seeing as you're limited to AGP then it will have to be an ATI card as nvidia have'nt released any agp cards since the 7xxx series and ATI have AGP cards available in the 4xxx series (only 1 generation old and some are still quite good). here is what ebuyer has to offer at the moment.
http://www.ebuyer.com/search?sort=pr...imit=10&page=1
i'd probably go for a 4650 or 4670 but it does depend on your budget and what you are currnetly running in the rest of your pc you might not get the full potential out of the graphics card if, for example, you cpu is quite slow it will cause a bottleneck and hold back the GPU.
What is the rest of you're system spec?