The University of California-Berkeley has been streaming videos of their courses through their site webcast.berkeley since 2001. In 2006 they became the first university to podcast a significant number of their courses on audio, making lectures available as downloadable MP3s put up on RSS feeds that you can subscribe to.
Their podcasted courses cover science, psychology, engineering, and many other subjects. Podcasts of lectures are released throughout the semester and they also have an archive of all their previous courses which they've made available on podcast and streaming video.