Math Kangaroo (contests)
See Math (animations of number and algebra concepts)
Math and Movement (using movement as part of math teaching)
Norman Shapiro's "Geometry Through Art"
Alan Selby's "Appetizers and Lessons for Mathematics and Reason"
Game Theory Lecture Notes
Eric Weissteins World Of Mathematics (mathworld)
National Library of Virtual Manipulatives
NRICH Mathematics - monthly maths quiz and more
ilemaths.net French Maths Site - Island of Mathematics.
Bitesize maths (Scotland)
Computing Technology for Math Excellence mathematics (K-12 and calculus)
efg's computer lab Includes fractal pages and more on the sierpinski gasket
WWW Maths Virtual Library
UK Mathematics Trust Website
Puzzles from Maths For Fun
Maths for kids age 6 to 11
A Dictionary of Units of Measurement
100 Great Mathematicians (a work in progress by Les Bill Gates)