Crooked Timber has a post on Who is the greatest (living?) academic speaker?. NewMexiKen hasn’t heard of most of the people discussed (mostly in the comments), but still thought this an interesting topic. Perhaps we can start our own dialogue here.
Two come to mind. Ten years ago I heard a presentation by Otto Kroeger on the Myers-Briggs personality types that had the group crying and laughing (mostly in self-awareness) simultaneously. He was as interesting, informative and amusing as any I can remember.
It seems to me that author/linguist Deborah Tannen was wonderful at a lecture I attended at the Potomac School when her You Just Don’t Understand: Women and Men in Conversation was a current topic. She had the audience, which was about 500 women and ten men, pretty well engaged as I remember it.