ITunes has been steadily expanding iTunes U, a collection of great, substantive content (often) from the world's great universities. I noticed that Oxford is now in the mix with a series of philosophy and fine art lectures. If you haven't explored iTunes U, get thee there. History, humanities, education, science and technology, literature, mathematics, social science and more are waiting for your click.
Treat your brain as well as your ears. And please share your favorites!