On Latinas, I find tanlines to be very hot on their boobs, not so much on their butts. There was a Brazilian girl a couple of years ago ("Carola", I think) who had really small boobs, dark olive skin, and some of the best tanlines on her boobs I've ever seen. And on top of it all, she was just flat out gorgeous... flared hips and all. Very hot girl!
Chica, of Chica's Place, also tends to sport tanlines. I think hers are very sexy too.
They don't look right on all girls, but on some girls I find them to be hawt!