The University of Oxford offers free podcasts of lectures by Oxford professors on this very fine website. Nine different divisions of the University are represented, including the Humanities, Medical Sciences, Continuing Education, and Life Sciences. By clicking on "show media items" under the description of each lecture, you can see all the titles in the lecture series, and choose from there....

Produced by the American Association for the Advancement of Science (AAAS), Science Update devotes itself to reporting a variety of scientific, technological, and medical topics via free online podcasts and radio broadcasting. Listeners can call in to the station or submit an online form to ask relevant science questions, which are then answered and investigated in 60-second podcasts or radio...