I just happened upon this list of free courses on the Daily Kos. There are plenty of courses covering many subjects at many top notch universities.
Of course most of these courses do not lead to any certification but a few do offer a certificate indicting a course was completed. Just as a sample I have appended one of a series of lectures by the head of the Yale Philosophy Department Tamar Gendler. The students do not seem to appreciate the humor of the t-shirt text with which she starts her lecture.
Aside from Yale, MIT, U. of Michigan, Notre Dame, U. of California and many others offer free courses. Outside the U.S. there are many resources as well including the University of Capetown. If you are just interested in learning and not paper credentials the Internet is a treasure trove of free quality material. Again the link to the list is here.