If your wallet is not burning a hole in your pocket and you want decent performance for your budget, find a cast off GeForce 4MX or Radeon 9000 from a later model G4 like the QuickSilver or MDD. These cards are reasonably peppy (they don't support Core Image, but they do QE fine), have more VRAM than you're likely to really need, and they'll work in your AGP 2x slot.

And they should be relatively cheap.

Peace,

Drew