I love listening to college lectures for topics I'm interested in but don't fully grok. I fell asleep in them back when I was paying for it and getting tested on the material. Now I can listen to the same lecture 50 times if I want. And no test.
An all time favorite: Lenny Susskind's Stanford open lecture series on Quantum Mechanics
Down side: sometimes I dream that I am trying to ask a question and the lecturer never notices. I have literally in the dream started running around terrorizing the room going insane screaming why does this professor not acknowledge my existence?!
Doubly hurtful when it's Lenny; he's such a comforting father-figure