iTunes U was created in collaboration with colleges and universities that were looking for ways to expand and enrich their curricula with digital content.Standford University lists 13 different categories of materials from Science and Technology to Health and Medicine to Personal and Professional Development. There is also commencement addresses from 2005 - 2007.
MIT has used iTunes U as one of the delivery channels for their OpenCourseWare initiative. This is a big investment; take for example the Electrical Engineering & Computer Science category, where MIT offers 161 tracks.
If you move outside the classroom, there are offerings from the New York Public Library, PBS, and others. You can find over 20 Jazz oral history video interviews and 13 audio presentations in the Small Business category at New York Public Library.
I have just scratched the surface of a deep, rich set of free educational content available to any iTunes user. I'm currently listening to a lecture of The World is Flat from Thomas L. Friedman as part of the MIT OpenCourseWare offerings, where Mr. Friedman talks about his book of the same title during the week it reached #1.