Nonprofit site Khan Academy offers short videos– each about 10 minutes long on average–explaining topics in math, science, history, economics, and some test prep. Although its collection of humanities videos is slim, Khan Academy has an astounding number of math and science videos, explaining everything from basic arithmetic to “partial derivatives of vector valued functions.” All the courses are conducted with a human instructor’s voice over a blackboard-style screen, so you never actually see a person. For some people, this arrangement might work better as a learning strategy because you can just focus on the facts and figures in front of you. Many of the videos have supplemental problem sets that you can use to practice the things you just learned.
The advantage of Open Yale Courses is that you get a much more comprehensive view of a single subject. The video podcasts are available for download from iTunes as well, and every so often (at Yale’s discretion) OYC will offer a batch of new, semester-long courses.
What’s great about both services is that they’re totally free and entirely streamed video, so if you don’t understand something, you can pause and rewind to hear the part of the lecture you find confusing.