Ok, the GeForce 256 and 256 DDR were the first GeForce chips to come out and generally at the bottom of the line.
Then there was a core change to the GeForce 2 core. The following products are GF2 based products, from worst to best.
GF2 MX
GF2 MX 200
GF2 MX 400
GF2 (This is the base model and the first to be introduced using the GF2 core)
GF2 Pro
GF2 Ultra
Then the GF3 core came around. There is only one chip based on the GF3 core, the GeForce 3 (now doesn't that suprise you?)
I think that should answer your question.
EDIT: Darn, all that typing for someone to beat me to the first reply. Life's tough.