There is interesting content from classrooms or lecture halls with subject from almost all the fields of science. It is a great opportunity for learning or reviewing material of high quality.

As I mentioned in a previous post, MIT has launched the MIT OpenCourseWare. Many of the school courses are available free online.
Berkeley also has launched a site with video and audio webcasts of classes.

If you have some free time to spend then free higher learning is a great investment.