The Khan Academy, established by Dr. Salman Khan of MIT is one of the best web educational site in the world. The website has a database of some millions of video lectures, meticulously made and simplified for the students of any class or age group. Dr. Salman Khan started tutoring his cousins in youtube, since when he gained popularity as a web video lecturer.
The lectures are fascinating and are presented so differently in front of the students that, a boy who never heard about derivative started doing calculus meticulously. The videos can be found in many languages and of varied subjects, not only about science. Even the texture and accent of Sals voice produce a good vibe among students. It is a completely free education providing site, where people can and must donate to make it more successful. Just login to https://khanacademy.org and I bet, you won’t be deceived.