Khan Academy:This is the most famous math video site on the Web. It has over 2700 videos, a large fraction of which are on mathematical topics ranging from beginning arithmetic to vector calculus. It also includes self-testing exercises and discussion boards.

Brightstorm: Over 2000 free math videos.

PatrickJMT: Just Math Tutorials. This site has nearly 1000 videos on algebra, arithmetic, calculus, differential equations, discrete math, linear algebra, probability and statistics, and trigonometry. Tends to be a bit more advanced than Khan Academy, with few videos on prealgebra topics.

MathTV: This site features math videos by textbook author Pat McKeague and six of his students. It has many free videos, but it also has videos of the examples in his textbooks, and those videos require a paid subscription. Topics include basic mathematics (prealgebra), algebra, geometry, trigonometry, and beginning calculus.

Mathtrain: Math videos created by middle school students.