I've gotten hooked on Teaching Company lectures--they're typically about 12 hours long, covering various topics (there's a link to the left that goes to Goodreads, where I've listed ones I've completed). I'm currently on a mathematical one--the proof just given is cute:
Hypothesis: Every natural number is interesting.
1. Suppose any natural number is not interesting.
2. Is there any natural number less than that number that is not interesting?
4. Well, what's the smallest natural number that isn't interesting?
5. Now, isn't the fact that that number is the smallest number that is not interesting... interesting?