For women, some Klingons -- although not when their boobs were showing! They seemed to have such noble bearing like with Grilka or Sirella. Not sexy in the shallow sense, but carried themselves very well. And also Ba'el (half Klingon half Romulan) who was kind of pretty and all.
And also Cardassian women who had that exotic look. Cardie men, not so much but the women... yep. Even though that blue on their foreheads is still quite reminiscent of pool cue chalk.
And let's not forget the Bajorans. Some anyway. That was just such a great subtle way of making someone look alien.
For men, I can think of many less on the non-human "sexy" front, actually which is ironic since I am a non-gay woman! I'll have to give that one some thought.
When in doubt, hug your teddy.