Here are the collections of sites with math, physics, engineering, and other sciences video tutorials. Some sites also contains non-science videos as well. If you find a site with more than 50 videos, please inform me so I could include it on the list.

Khan Academy – more than 2100 2600 not only for math but also includes other subjects such as economics, chemistry, physics and other fields. The math videos range from adding integers up to elementary calculus.

Brightstorm – more than 500 math videos in algebra, geometry, Precaculus and Calculus.

Just Math Tutorials – more than 1000 videos on algebra, geometry, trigonometry, calculus, differential equations, and linear algebra

MIT Open Courseware – videos about math, engineering, sciences, and other fields.

Free Video Lectures – more than 700 (excluding Khan Academy’s which they also listed) videos. Videos include single variable calculus, multivariable calculus, vector calculus, probability and statistics, algebraic topology and more. Some are actual class videos.

Math Playground – more than 70 videos for high school mathematics. Topics include integers, algebra 1 and 2, and geometry.

Gresham College Public Lectures – more than 100 public lectures about mathematics particularly history of mathematics, computational mathematics, everyday mathematics, mathematical puzzles, and more.It also contains hundreds of more public lectures in astronomy, biology, physics, other sciences, and other areas such as law, arts and literature, medicine, music, politics, and more.

One of the best videos about mathematics I have seen in the internet are from Khan Academy. Khan Academy offers more than 1100 downloadable videos for free in Algebra, Geometry, Calculus, Differential Equations, Physics, Linear Algebra and other fields. Shown below is one of their mathematics tutorial videos discussing the concept of slope.

If you want to see the list of all their free videos, click here.

If you are a teacher, you can watch the video above and refer it to your students. But did you know that it is quite easy to make such video?

If you want to learn how to make a video such as the one you have seen above, I have posted a tutorial about it here.

Update:

Here are some other sites offering math videos for free.