IMHO, the NVIDIA and ATI cards are the best way to go for OpenGL. The question is, how much you want to spend…
ATI Rage, Rage II, Rage 128 and similar are not really up to date anymore (the Nvidia counterparts would be Riva TNT and TNT2) but sufficient for ‘smaller stuff’ and available used for under $100
Today’s high end cards are Nvidia’s GeForce II, GeForce III (there’s no real competitor to the GF3 from a technical point of view), and the ATI Radeon. These cards can do a lot more (as far as functionality as well as raw performance goes) than the above mentioned, but of course, are significantly higher priced.
Another alternative you might want to look into are Matrox’ G200/G400 cards (good cards from what I hear, but the driver support is supposed to be not as good as with Nvidia and ATI). As far as the best card driver support and updates goes, this prize I personally would definitely award to Nvidia
Take a look at the card specs and prices, and decide which would be best for you.