I have a G4 MDD (dual 867 Mhz and 1 gig of RAM) with a GeForce 4MX. I am considering replacing the card, and would like to get some advice as to what to buy.
Why are you upgrading. For gaming, or another reason?
If ADC isn't necessary, i'd recommend getting a flashed Nvidia 6200 or 6600 as they are quite fast and have SM 3.0. There are also Radeon 9800's that can be installed I believe which are quite speedy.