Free Graph Paper: create and print graph paper
Wolframalpha: Answer questions, do math, instantly get facts, create plots, calculators, unit conversions, scientific data and statistics, help with homework—and much more. It may be helpful to enter portions of a problem or enter the problems in steps.
Mathway: Math problem solver
CoolMath: A variety of games, puzzles, calculators, and math help. Don't let the graphics fool you. It goes up to calculus level math.
IXL: Loads of practice problems