I think after MOS is ported to Mac Mini the next best choice would be the Powerbook(not iBook)
It got a G4 with up to 1,67Ghz and a Radeon 9700(the question is if it's possible to make a Driver for the R9700 that support 3D?)

@ CountRaven: Afaik the 8610 and 512* are used only on some expensive Dev-Boards.