Without question the X850 pro. How much? Online in USA? Link? (I'm interested)
You can get 6800GS here for $200, which would be a very good buy for a X850 pro AGP now.
The 6800GS might take a few games like Doom3, but the X850 pro is near to the 16-pipe X800XL and 6800GT, and definately above a X800 pro, X800GTO, 6800GS AGP.