Are you interested in programming? Do you want to learn what separates serious professionals from amateurs? There are a variety of things that can qualify, but to really understand computer science I highly recommend "The Wizard Book"1. Known formally as Structure and Interpretation of Computer Programs (SICP), this $75.00 MIT textbook is worth every penny for someone who's serious about his or her craft. Of course, that's a fair amount to shell out just because I said so. So download SICP for free. However, that's not all. If you can't afford the 30K per year tuition, download professionally produced video of the lectures for free too. Be prepared to learn Lisp and Scheme.
Irrelevant side note: Today is the 18th anniversary of my moving to Hawaii and subsequently becoming homeless. Ah, memories.