Radeon 8500, faster then the GF3 Ti200 with a better feature pretty much across the board, along with numerous little extra's in the way of superior FSAA visual quality, better DVD playback, better 2D visual quality in most cases, a better anisotropic filtering algorithem, slightly better TV-Out capabilities, DVI-Out, TV-Out, HydraVision by default. etc.
The GF4 Ti4200 looks to have another month in a half before it hits the market, and latest rumours all seem to have it being delayed until ATi's RV250 core hits so I wouldnt count on it anytime soon.
If you can wait a few months then the Radeon 8500XT, and GF4 Ti4200 are all coming down the pipes... but it's questionable when they will appear.