EdX
EdX offers interactive online classes and MOOCs from the world’s best universities. Online courses from MITx, HarvardX, BerkeleyX, UTx and many other universities. EdX is a non-profit online initiative created by founding partners Harvard and MIT.
MIT OpenCourseware. Basically, MIT gives you last year’s course lectures totally for free. If you want this year’s courses and access to professors, you need to attend the school.
Udemy has a variety of free and low cost courses. Offers change so check in once in a while to see if you can catch what you want at a good price or for free.