Coursera: https://www.coursera.org/
Harvard and MIT: https://www.edx.org/
MIT: http://ocw.mit.edu/index.htm
Stanford: http://online.stanford.edu/
English and German courses: https://iversity.org/
Future Learn: https//www.futurelearn.com
Open U: http://www.open.ac.uk/about/main/
Learn new languages: http://www.duolingo.com/
Learn how to code: http://www.codecademy.com/
Courses and audio books: http://www.openculture.com/