Cool Math
Coolmath: Precalculus Basic Formulas to Know
This CoolMath resource provides an introduction to some Precalculus formulas.
National Council of Teachers of Mathematics
The Math Forum: Famous Problems in the History of Mathematics
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...