Kenshi, Kai, Reiko, Tanya (prefer her moves from 4 but her costume from Deception), Fujin, Bo Rai Cho, Quan Chi, Frost, Drahmin, Hsu Hao, Kira (but only the pigtailed costume, her more mature costume lacks irony), Dairu, Hotaru, Havik, Shujinko, and the Armageddon version of Meat is pretty cool.
I more or less like every character from MK. The only ones I ever took issue with were Mavado, Jarek and Chameleon, and even they could be made to be cool. I hope to see a lot of the later characters make a return in MK9 as dlc, or in MK10. I think a good number of them would work better in a 2D plane anyway.