Okay, so so far there are:
Githyanki - original offshoot of the peoples enslaved by the illithids; currently live in the Astral Plane. See the Expanded Psionics Handbook, Dungeon #100, and Dragon #309 for more details.
Githzerai - original offshoot of the peoples enslaved by the illithids; currently live in Limbo; see the Expanded Psionics Handbook for more details.
Pirates of Gith - offshoot of the githyanki; currently live in wildspace. See 2E's Spelljammer Monstrous Compendium Appendix (MC7) for more details.
Athasian Gith - offshoot of the githyanki; currently live on Athas; see the 2E Dark Sun adventure Black Spine for more details.
Githvyrik - original offshoot of the peoples enslaved by the illithids; currently more a group of inidividuals than a true race. See Dawn of Night by Paul S. Kemp for more details.
Githzada - original offshoot of the peoples enslaved by the illithids; currently live on the Astral Plane. Created by Fiend Games. See Gaming Frontiers issue #0 for more details. (As an aside, as near as I can tell, this is all there is about the githzada; Fiend Games seems to have folded not too long after this was written, and their Project Planeshifter line seems to have died out before becoming more than a handful of titles and synopses, along with that one preview article.)