The X850's are a nice card, actually anything in the X8xx series (X800PRO ,X800XL, X800XT , X800GTO and GTO2 ) will still do a good job , espessially when playing games in D3D ( direct3d). In openGL it seems Nvidia has a clear performance advantage . I just did some quick checks on X8xx series cards at two vendors ( tiger direct, Newegg) and it seems that the AGP versions of those cards are starting to dry up ( atleast on those sites) .
If i was buying AGP in that price range i would look for:
Nvidia) 6800 GS ,GT, Ultra,
Ati) all listed above and including X850pro's and XT's .
I did read somewhere that Nvidia was going to produce the 7600GS in AGP , if so that would be a great card depending on the price. The lowest ive seen 7800GS's for are around 250 with a mail in , but if your going to be sticking with AGP for awhile , it's prolly the last higher end card AGP will see. 38