I think the most fascinating thing on iTunes is the "iTunes U" part, where you can get sound/video recordings of hundreds of courses from several universities/education centers all around the world (you can find all these items through the net, but in "iTunes U" its all grouped and packaged in a wonderful way).
These days I am listening the Benjamin Polak's Game Theory lesson at Yale (at long shuttle hours to/from work) and I can easily say he is a great instructor. He talks about all main topics through the courses in an easily understandable way with interesting examples that takes your attention immediately. And also he has a great sense of humor, don't be surprised if you find yourself laughing loudly while listening his lessons.
Last words, if you are interested in "Game Theory" dont miss this chance.