When I was searching for online teaching material on cancer, I stumbled on the MIT open course Introduction to Biology. It was taught by Eric Lander and Bob Weinberg in 2004. The two are pioneers in genomics and cancer biology, respectively, and both are members of the National Academy of Sciences. They delivered over 30 amazing lectures (with publicly available videos) on introductory biology. They explained biology in simplistic yet fascinating story telling style, and only used chalk without any powerpoint slides. The concepts they explain are super clear and and their messages definitely stick. You could totally see their passion for biology and their charismatic style.
Most elite universities value faculty research over teaching. I always have special respect for faculty who care to teach well in addition to doing good research. Bob and Eric epitomize this type of faculty. I wish I had learned Introduction to Biology from them when I was a freshman in college. As a matter of fact, I would urge all biology majors to watch these videos.
Actually I just found that the videos are hosted here, which also has many other interesting free online courses. E.g. Rafa told me about this Machine Learning course from Stanford. Hooray! I will be going to these lectures for sure! Many of the courses are given a rating, e.g. the Machine Learning one is rated A. Great resource, I hope they keep adding more material over time.