Personality-wise (and I know this sounds cliched) I like girls with good sense of humour. I like people who can make me laugh. She'd also need to "get" my sense of humour, or she'd be

a lot of the time.
I like people with strong views and opinions as long as they're not belligerent about them. (She might, for example, be a vegetarian and I will respect her beliefs, but she'd have to respect my right to get a BigMac whenever I wanted one.)
Someone with whom I have shared interests is good, but I'd also want her to have interests that were totally her own, as I don't think it's good or necessary for a couple to do everything together. I also tend to find someone more interesting if they have interests that are outside my usual scope of experience.
As for looks, I don't really have any hard and fast preferences. I suppose if I look at women I've been most attracted to or been in relationships with, she'd have dark, pretty eyes (brown rather than blue), longish dark hair (shoulder length or longer) and be of average height or above. Oh, and probably wear glasses.