The New York Public Library has lots of free audio and video (and text!) on iTunes! See: NYPL on iTunes U. [1], by Barbara Taranto, NYPL, April 8, 2008.
If you have iTunes, here are some direct links to get you started:
- NYPL at iTunes
- Live from the NYPL [2]
- Slate At 10: Online Media and the Future of Journalism [3] (text)