Greenberg is great but my favorite professor of all is Rufus Fears of the U. of Oklahoma. He's an unapologetic advocate of the Great Man (or should I say Great Person) theory of history and is a spellbinding lecturer. He just released a new course on Great Books which I plan to pick up soon.
Sometimes the kids get a great deal out of them too. I think they miss Greenberg this semester, since I'm not teaching anything interdisciplinary with music.
Let me know which are your favorites, and I'll check out the Teaching Company sales.