Church. Specifically, a weeknight church activity in which a member of my congregation gave a 45-minute lesson on finances that was based heavily on MMM. She gave us a handout with links to some MMM blog posts, as well as a few other financial sites I didn't find as useful, and she gave us a summary of the most important things for us to know (i.e., live frugally and responsibly, use tax-advantaged accounts where possible, and throw everything else into index funds). I was already saving a lot and living very frugally, but I'd been too intimidated by the stock market to make any investments, so it was very helpful finding out about index funds and so forth.
