Website
National Council of Teachers of Mathematics

The Math Forum: Famous Problems in the History of Mathematics

For Students 9th - 10th
On this site, there are several math problems to explore and solve. Look through some solutions by famous mathematicians and expand your thinking about some interesting math concepts. Teachers of elementary grades may want to use this...
Website
Wolfram Research

Wolfram Math World: World's Most Extensive Mathematics Resource

For Students 9th - 10th Standards
MathWorld provides a huge mathematics encyclopedia detailing the concepts of geometry, algebra, calculus, discrete math, number theory, and other math topics--complete with formulas, diagrams, examples, and references for thorough...