Without going in excruciating detail, I would argue that he is an INTP, based on Keirsey's temperament sorter and the cognitive function model. He obviously views the world in a very rational way, questioning ideas and/or natural phenomenon until he arrives at a satisfactory answer.
I used to find his strict adherence to atheism a bit too close minded, but if you watch enough of his debates you will find that he is more accepting of discussing concepts of gods that are impersonal in nature. He is tolerant of the pantheist, Spinoza god and detests the Judeo-Christian god.
He is a skeptic in nature, but he tends to be rather polite about it for the most part, as opposed to the more inflammatory Hitchens.