This is something I discovered a while back, but it does not seem to have caught much attention: the Massachusetts Institute of Technology (M.I.T.) has put online its entire curriculum of more than 2000 courses. You can download reading lists, lecture notes, exams, and in some cases, videos. There is a page showing the most visited courses, from which I selected the first, entitled "Problems of Philosophy" (taught in Fall 2005). From that page I could go to a listing of selected lecture notes for the course, including topics such as the existence of God, the problem of evil, Pascal's wager, rationality and belief, mind and body, free will and determinism, and morality -- a veritable treasure trove for a budding philosopher. (Isn't it funny how we are not particularly attracted to the problems of philosophy until we get older? I suppose the reason is that until you have lived a good deal of life, you are too busy to examine it -- or else you just want to tell everyone else how they should live.)
You cannot get any kind of course credits online, and there is no interaction with the professor, or other students. But MIT's curriculum -- heavy in math, science and engineering, of course -- is still broad enough to have something for everyone (try, for example, the Editor's Picks page). And if you do partake of the offerings, be sure to return the favor with a donation to keep this marvelous program going.