Khan Academy

Khan Academy has thousands of free online lessons available in mathematics and many other subjects. Many of the lessons are also accessible on YouTube. The Khan URL is https://www.khanacademy.org/.

MIT OpenCourseWare

The MIT OCW site contains lecture materials, problem sets, and even entire taped course lectures for over 1,800 MIT courses. Supplementary materials available vary by course. In particular, material covered includes MIT's first semester course in calculus. There is also an excellent course in differential equations delivered by Arthur Mattuck. Unfortunately, Walter Lewin's Physics 8.01, Physics 8.02, and Physics 8.03 lectures have been removed from the OCW site. These briliant videos are the lectures Lewin gave while he was teaching the three-semester basic physics sequence at MIT. However, the whole Lewin lecture series is still available on YouTube.

Wolframalpha

The amazing wolframalpha website is an online computational engine that solves equations, simplifies algebraic expressions, performs calculus computations, and generally gives users all sorts of numerical support.

General video math lectures

A general site for online math and physics help is http://linuxfreak87.googlepages.com/. The site has several dozen links to video lectures, course materials, and even online editions of textbooks. Topics range from elementary algebra thru graduate level mathematics. Included are links to online video presentations of complete math courses, including single- and multi-variable calculus. A word of caution: The site is apparently not updated regularly, and some of the links don't work.

Algebasics

The Algebasics website offers quick, detailed explanations of how to do many types of basic algebra problems. The tutorials work best when your computer audio is turned on. After you click the Algebasics link, you will see a list of topics. Click on a topic and you will see a list of problems. Click on one of the problems, and you will see and hear it done out in detail.

Purplemath

The Purplemath lessons Index provides links to an big collection of Purplemath algebra lessons. The lessons are well-written and are illustrated with good examples.

Mathcasts

Mathcasts are movie-type solutions of calculus problems. Solutions are given slowly and in detail with voice-over explanations and good graphics.

Midnight Tutor

Midnighttutor.com has videos of teachers solving dozens of different types of calculus problems. If you get *really* stuck on something, check out the list of videos and see if you can find a similar problem. The site is also good for getting extra insight into tough topics. You can just sit down for a while and watch problems of some particular type being solved and explained. I found the related rates and integration videos particularly helpful, although the teachers do occasionally come up with a solution that is way too complicated. If you can't find a video to match your problem, you can e-mail the problem to Midnight Tutor, and they say that they'll send you back hints. (I've never tried this, so I don't know how long it takes to get a response.) The e-mailed questions are the sources for video topics. If a question is interesting enough, they'll make a video explanation of it and post it to the site.