Togruta. Togruta, Togruta, and did I mention Togruta?
I'd also love Kel Dor. In the very first early trailer for TOR the first thing we saw was a Togruta Jedi and a Kel Dor Sith fighting, then there were rumors that both species would be playable and I was all set to finally play as both of my two favorite Star Wars species... And they never came. Their absence is literally the driving force that kept me from getting into this game until it went F2P, I just couldn't get into the idea of playing as the Human Skittles that they gave us as our species options.
At this point I've pretty much giving up on any seeing the more interesting species of the Star Wars universe, as it is Cathar were a huge disappointment. There's hardly anything in the game to acknowledge that they're a unique species, I doubt we'll ever see anything more complex, such as a being with horns, head ridges, etc.