AGP 8x is backwards compatible with 4x, so you should look for those. And AGP is being replaced by pci-e, but on newegg, its like 400 pci-e compared to 100 AGP cards to choose from. Still a pretty good selection.
If you want the absolute best AGP solution and are willing to put forth several hundred dollars, the top of the line are the ATI Radeon x1950 (pretty sure this is in agp flavor) and the Gainsward Nvidia GeForce 7800.
For around $100-200 you get into the Geforce 7600-7800 and high end Radeon x1k series.
Mid ranged gaming cards are around $100 and include nvidia 6600-6800 and 7300(though the 7300 is considered low end, its still in this price range and has good performance) Note I have a 6800 agp and it plays any game i throw at it very well (mostly high settings) and gets me a 3dmark06 score of around 1500-2000. On ATI's side, there is the x700-800 and such.
Low end cards can be had at around $50-$100ish and are the 6200, x300 and similar. Can still play some new games at decent settings.
I would definately not go any lower than that(like to the 9xxx ATI or Nvidia FX series.)
The best place to compare video cards is http://www.tomshardware.com/graphics/index.html
They still compare AGP and have kind of new 'best AGP card for the money' things and VGA charts.
Edited by nforce, 04 February 2007 - 01:50 AM.