I'm admittedly biased, but KEL DOR!
They live on a planet that is nestled between two black holes making it a place that most people will never see and a place you wouldn't expect to find life, let alone sentient life. Virtually no one has ever seen what they look like under their masks because they can't take them off outside of Dorin's atmosphere. The masks give them an intimidating, emotionless quality that is so fun to RP with. They have their own force tradition (Baran Do), have produced some very powerful Jedi, are natural telepaths, and have an awesome black and white view of the world.
That is one awesome species!