National Council of Teachers of Mathematics www.nctm.org
Illinois Council of Teachers of Mathematics www.ictm.org
Internet Mathematics Library http://mathforum.org/library/ 
Geometry http://library.thinkquest.org/2647/geometry/geometry.htm
Math Puzzles www.mathpuzzle.com
Logic Problems www.geocities.com/Heartland/Plains/4484/logic.htm
Math Reference Tables www.math2.org/index.xml
Ask Dr. Math http://forum.swarthmore.edu/dr.math/dr-math.html
Cool Math - Just for Fun www.coolmath.com
Manipula Math with Java www.ies.co.jp/math/java/index.html
Math Forum
Free Math Tutor