Independence is a big one for me. For example, I would find it VERY difficult to date someone who still lives at home.
Self-confidence ... I like a guy to be able to be himself, and know what he wants, and not care too much about other peoples' opinions of him, e.g. what his friends think, etc. Someone who can is openminded and can take on board advice and opinions, but who has confidence in their own beliefs and ideals.
I can't ever see myself dating anyone religious. I just can't understand that mindset, and anyways it would cause all sorts of problems long-term.
I couldn't date a workaholic. Been there, done that, never again! I'd much prefer someone who works to live, rather than vice versa.
A bit of a shallow one
But I don't think I'd date someone shorter than me. (I'm only a shortarse myself though, so that's an easy one!)
I don't think I'd date someone involved in drugs. Never done them myself, and it's just not something I'd want to be involved with. (Smoking and drinking are fine!)
Jealous, possessive, controlling guys are the biggest turn-off in the world to me. I've never been involved in that sort of a relationship, but I've seen friends who have, and it's scary! I'd run a mile if I ever saw a sign of any of that sort of crap. It just shows a complete lack of trust and respect, in my opinion.
Other than that ... It's all about this mysterious "spark" that everyone talks about. If that's not there, then no matter how perfect the person is on paper, there's no point in trying to force a connection that doesn't exist!