On the Web
Chosen as one of the American Library Association's best websites for young people, this site offers easily searchable practice questions in all areas of math up to Grade 12. Got an answer wrong? This site shows you how to get it right.
Brightstorm has a great collection of videos on an array of different subjects, all led by skilled teachers. The math collection has videos of lessons and problem-solving techniques for everything from Pre-Alegebra to Calculus.
With thousands of free practice questions and study guides on everything from basic math to calculus, Cliffsnotes Math is an awesome, free resource to keep you from being stumped in math class.
Do you feel like everyone in your trigonometry class is speaking Greek? Check out Sparknotes Math to get you back on track. With graduated, step-by-step study guides and tons of free problems (with solutions!), this is a great resource to give you a little boost in everything from pre-algebra to AP Calculus BC.