I would highly recommend ATI Technology's RADEON (AGP or PCI version) because it has 32MB of DDR-SDRAM and a hardware transform and lighting engine called the Charisma Engine. It should give you the performance you require.
the best that you can get if you have a 2X AGP Mac is the Radeon. The best you can get if you have a 4X AGP Mac is the GeForce 3. I use both with Lightwave 6.5, and they are both sufficient - much better than the 16MB Rage 128Pro.
I still wish that SOMEONE would make a high end card like 3DLabs Oxegyn for the Mac. Until someone does, the Mac market won't be taken seriously for 3D work.