Smart is a given. So are clever and dedicated. But most of all, I look for people who are highly collaborative. Isolated, ego-driven introverts tend to create the programs they envision, not the ones I need. We always make a place for the one-off eureka workers, but it's not in IT.
In my new position, we do something I have never done before. When there is a perspective hire, they sit with everyone in the department separately for a few minutes. This way we all get a feel of how they may fit in the department. Then we discuss any issues among ourselves and see if we all feel the same.