http://www.openculture.com/freeonlinecourses
If you just want one site with lots of courses I think this would be it.
http://ed.ted.com/
The ted website with educational videos that have a speaker and an illustrator. We've all seen these on youtube before.
http://www.mentormob.com/
People make playlists of things they want to teach. Kind of like youtube tutorials except specifically for education.
http://www.memrise.com/
Uhm. Claims to make learning fun. Primarily seems to teach languages
http://learni.st/
Reddit's TIL where the people posting articles are paid to post them. Social Mediarized Education.
http://openlearn.open.ac.uk/
UK courses free
http://ureddit.com/
If reddit users made courses...
http://www.academicearth.org/
More free courses
http://www.youtube.com/education
What? Youtube has an education section?