Based on the current looks of tauren, I believe there are a total of 19 different skin choices for male tauren, and 11 skin choices for tauren females. Many similar tones will share the same bear and cat forms though. We're looking to release a break down of the tauren skin tones and night elf hair colors, as they correspond with the different cat and bear form color options, shortly after the new night elf cat form art is released.
So don't worry guys, you won't have to jump on the PTR to fiddle with the barber shop to pull together a list of the different colour combos. Blizzard should be providing one soon.
Edit: here they are (created by MMO Champion, based on a text list released by Blizzard):
Thanks Beru - I'm in Australia so updates always happen while I'm asleep :(