Math Dictionary This site allows view math terms and provides illustrations.
Hot Math Hot Math will give explanations of how to work the odd problems in your math book. This is now a subscription site.
Dr. Math This is a site that will allow you to choose different areas of math and find out how things are done. Fact Monster Math One more good "how to" site. This site doesn't have a whole lot of relevant topics, but it does have some interesting ones. It also has some games and other interesting information about math.
Math Help This has lots of good material in it. The page that I am taking you to gives you a list of classes to choose from that can help you with your homework, from explanation of concepts and examples to practice quizzes.