iTunes University was mentioned in an article in the January edition of the AARP Bulletin received through the mail. I do think it's the first time I ever found anything useful in the bulletin (a happy surprise). Here's the link, with my disclaimer that the link may or may not work:
The New U.: How to Learn Just About Anything Online for Free - AARP Bulletin Today
There are other sources mentioned in the article, but I found the real gem to be iTunes University. As the article mentions, you will need to download free iTunes software (if you don't have it already), but everything in the iTunes University is free. The list of universities contributing material is impressive, and the courses and lectures are mind-boggling. Not only universities provide material; institutions such as the New York Public Library offer lectures, as well.
Some courses and lectures are video and audio; some are just audio.
Hope this post becomes a happy surprise for someone else (and you didn't need to read through the AARP Bulletin for it!).