I've added a link to Academic Earth in the sidebar. I found this very interesting site from the Slate article "How To Go To Harvard For Free."
Academic Earth has a great and growing collection of videos of lectures and courses from Berkeley, Harvard, MIT, Princeton, Stanford and Yale.
It's an absolutely delightful treasure trove of information. You can view lectures on a diverse topics by subject, universities, instructors and playlists selected by the editors. You can also make up your own playlists by adding lectures you like to your favorites.
Here's a list of what I'm currently exploring -
Two other good places for learning or picking up ideas are Open Yale Courses and Stanford ECorner.