Geforce 2 easily.
Following the nVidia line, from (popular) geforce 2 boards, it basically goes:
geforce 2 mx
geforce 2 gts
geforce 4 mx
geforce 3 (ti200, then ti500)
geforce 4 tiN (where the higher the N, the better
The Geforce 2 cards are ancient though - my integrated Geforce 2mx on my nForce is preventing me from enjoying Warcaft III in all its gaming goodness, as well as Dungeon Siege. If you have the money, a Geforce 4 Ti4600 is worth it, although the recently released Radeon 9700 stomps upon it like nothing.
(Both are expensive cards though...)