To put it simply: A girl who's similar enough to me that we have common ground to connect on and yet different enough that both of us don't get bored out of the lack of something new.
I'm also a generally quiet person and of small stature so I suppose I'd like somebody who'd match that. I like people who are shy/quiet at first but get more open as you get more comfortable, like me!
I'm not shallow enough to let things like hair color/ethnicity/bust size/etc be deal breakers for me, even though I do have my preferences (i.e. European, pretty, lighter colored hair or redhead, etc), I'm not a looker myself so I'd be asking too much if I thought of this stuff as mandatory, lol.