Most of them are really good. Here's a partial list of the ones I've enjoyed:

- Machiavelli in Context (probably the best course of theirs I've listened to)

- Big History: The Big Bang, Life on Earth, and the Rise of Humanity

- Conquest of the Americas

- Early Middle Ages, High Middle Ages (same lecturer--one of the best)

- Foundations of Western Civilization I and II

- History of Ancient Rome

- Birth of the Modern Mind

- Story of Human Language

- History of Science from Antiquity to 1700