Science
iBioSeminar
http://www.ibioseminars.org/
ioSeminars features lectures and videos about biology, ecology, health (and more) that begin with broad introductions and progress to specific research. Most videos require QuickTime.
Science Tube
http://www.science-tube.com/
Test Toob
http://www.tubechop.com/ Join a free community of everyday scientists! Test Toob is an ultimate online lab where videos can be uploaded, viewed, and rated. Browse the site for great ideas, and learn from information on creating great videos. See what other students are doing. "Experiment Ideas" offers great videos for experiments for students or classes to try. Visit "Test Toob 101" to explore student generated videos, peruse a list of experiments, upload or share, and view 5 steps to safety for experiments. Tabs at the top provide easy access to information: "Home," "My Workbench," and "Community." Visit the Community page to view videos and comments. Video categories include Chemistry, Engineering, Life Sciences, Mathematics, and Physics.
Khan Academy
http://www.khanacademy.org/