Straight, white teeth, nice lips (not so thin they disappear when you smile), dimples help, a genuine smile (not those fake "cheese" ones) and when your eyes sparkle.
I agree with this. I have nice teeth, but I have pretty thin lips. I wish they were plumper. I'm not a fan of dimples, though, even though I have them (maybe because I have them?). Tman's are handsome, though.