Einztein is a great site that provides a listing of free online courses from around the world. The courses include text, audio, video and multimedia. The courses are all recommended by the team based on the quality of the course. They don't host the courses or create them, just link them in a searchable database and allow for comments and suggestions.
The catalog is searchable and includes courses from Stanford University, the British Museum, Cornell, Duke, MIT and many more. You can search by topic and even filter by course provider and media type. There are recommendations and reviews of the courses and even some suggestions for related courses.
They are working on expanding Einztein to have more of a "social network" feel and incorporate more suggestions, comments, and even allow people to work together and get help for the courses.
This could be great for teachers looking to expand their knowledge, to use in the classroom or to have students use it as extra help. I've viewed some of the material and it is very good.
Here are some examples of some of the courses:
