I've learned so much from Khan Academy – not just whatever is explained by the video I'm watching, but different ways of educating people as well. In fact, I helped out with tutoring basic math a while back and I struggled at first because I didn't realize how much I wasn't teaching simply because it was second nature to me. After watching a bunch of Khan Academy videos on the same topics, I found different ways of explaining things, and was much more successful. Khan Academy has really challenged my own way of thinking about many things, math in particular.

It's a great resource, and while I don't use Khan Academy much these days I still donate $100 every year.