Read a lecture on Corporate Finance from a professor of New York University; learn more about Geophysics from a professor of Cornell University. Enhance your knowledge about Organic Chemistry from a professor of University of Toronto, and get more techniques in Probability and Statistics from professors of Imperial College of London.
Varsity Notes contains lectures ranging from Accounting to Sociology (Biology has the most number of entries). They are available either in pdf format, MS Powerpoint or HTML. College professors and students might find this site useful, although I've noticed that most of the lectures came from professors from universities in
Whatever field you want to study, Varsity Notes shows us that learning knows no boundaries. So go ahead, make your learning "world-class" and maybe a gaining a little knowledge might not be dangerous at all.