3dfx Voodoo Graphics for making 3d acceleration viable / mainstream (there were other 3D cards, but too many flaws). That will always be top dog for me and was also the first 3D cardI owned.
9700pro and 8800GTX were very good / long-lived cards for their time, essentially cards I wish I'd bought. In the old days cards were really starting to struggle mid-way through the next generation but they were two cards that you could viably be using 2 generations on (I know that's commonplace these days, but the pace of change was much quicker back then).
You could maybe make a case for the influence of some lesser cards, e.g. those pushing the envelope on quality such as the Matrox G200 (bump mapping), PowerVR (antialiasing), TNT2 (32bit colour) etc