As far as intelligence goes, I don't know how to measure that. Here is my best effort.
I would prefer someone that is at least on my own academic level, I am not saying that they have to have an advanced degree in a science, but they should be reasonably well read and are capable of inductive and deductive reasoning (Hell, I'd probably settle for them knowing the difference!) They must be willing to think, and be interested in expanding their knowledge. They must also be somewhere near my maturity level.
Lets face it, as a guy I pretty much have a built in disadvantage in the dating game, so I better not discount 2/3's of the field out of hand. After all, I have dated girls that are, well, um... I'll say vapid to be nice, and it was not all that bad.