Khan Academy – Over 3,200 videos that cover topics ranging from arithmetic to physics, finance, and history. Also includes a number of computing tracks, including Hour of Code programs. Learn what you want, when you want, at your own pace.
edX offers over 650 courses in computer science, the humanities, and math, with over 1,700 faculty and staff from the likes of Harvard, MIT, Berkley, Caltech, and the Sorbonne teaching and discussing topics online. Began as collaboration between Harvard and MIT to bring some of their signature courses to anyone with a computer.
Access materials from over 2,000 courses from the Massachusetts Institute of Technology, including courses in Technology, Science, Economics, Mathematics, and Law.