I recently learned about a great learning tool called edX. They offer some really interesting online courses from various universities, such as UC Berkley, MIT, and Harvard, for free.
There is currently a course called Food for Thought (CHEM181X), taught by three professors at McGill University (Montreal, Canada)., covering the basic science behind food and popular issues related to food and health. There are several short video lectures per week, complemented by quizzes and surveys. Your level of participation is completely up to you; there are assignments and an active discussion board for the course as well. Perhaps one of the neat things about this and presumably all edX courses is the diversity in “students”. Just scanning the classroom introductions on the discussion board, there are people from Montreal to California to Mexico to Lebanon.