Wolfram Research
Wolfram Math World: Geometry
This MathWorld tutorial provides detailed overviews of the concepts and theorems associated with geometry. Most of the Math World sites are extensive and some require higher math knowledge to understand, links to terms and topics are...
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...
Other
Science Gems: Mathematics
This site has many links to math topics including pre calculus and calculus
Other
University of Evansville: Max Noether
Clark Kimberling provides a brief biographical page on Max Noether, who is one of the founders of algebraic geometry.