At Gator Freethought's 2nd meeting, Prof. Witmer gave a talk entitled "How To Think About (the Lack of a) God." Dr. Witmer argued above all else that we can (and should) rationally inquire into the question of God's existence—it is not a "matter of opinion" or "merely a matter of faith." Such inquiry, he further argues, undoubtedly leads one to atheism. Dr. Witmer also considers atheism in relation to theism, agnosticism, and other labels we might use; he discusses skepticism and the belief that faith ought to end the conversation, both of which he considers potential impediments to rational discussion; and finally, attacking teleological arguments for God's existence and defending the Problem-of-Evil argument against it, he argues that atheism is the most rational position one might hold. For Dr. Witmer's abstract of his talk, see here.
The video is embedded below, or you can watch it at the GF site here, or at GV.