Playlists of full lecture series for dozens of courses.

Departments with content here include:
Astronomy
Biomedical Engineering
Chemistry
Classics
Ecology and Evolutionary Biology
Economics
English
History
History of Art
Italian Language and Literature
Molecular, Cellular and Developmental Biology
Music
Philosophy
Physics
Political Science
Psychology
Religious Studies

See also the Open Yale Courses web site, which opens with:

Recorded lectures from professors at various universities. Categories include chemistry, history, maths, biology, sport, law, crime & forensics, physics and psychology. Also, a topic tag cloud.

In June 2010, they announced they are working on a full site redesign, which should help clean up the navigation and interface. (While not terrible, it isn't great).

Relatively small site (compared to MIT, for example), but has some interesting stuff. Keep an eye on this one.

Just when I was ready to dismiss YouTube as the place for short, home-made clips of people's cats and teenage pranks, Google buys YouTube and adds a host of features, improved indexing, cleans up the copyright management, and now adds new, functional viewing page features (March 2010).