The first, which is quickly becoming famous is Salman Khan’s http://khanacademy.org, which extensively uses YouTube to provide what he calls “asynchronous learning”. Over two thousand videos covering a wide array of subjects, with particular strength in math, economics, and science. He also has over 60 videos on astronomy and cosmology. At about ten minutes each, the offerings are fairly near 400 hours of educational material. The site also is beginning to add assessment tools and there are some schools in the Peninsula that are trying it out as a complement to their standard materials.
The second, which I only heard about today, is http://quizlet.com, a flash card creation tool, that actually does several things I’d wanted to do in Flash, namely games and tests with packages of material. But perhaps the coolest aspect of this site is that the community is building these flash card sets, and thus there are literally thousands of sets. Also, your progress can by measured against the community: speed tests are ranked, items with the most errors are shown, and so on.
Both are currently free. Let’s hope they stay that way!