Free math worksheets All grade levels and skills http://www.math-drills.com/
websites linked to lessons grades K-5 http://www1.center.k12.mo.us/EDTECH/everydaymath.htm
math dictionary http://www.amathsdictionaryforkids.com/
interactive activities from NCTM http://illuminations.nctm.org/
national library of virtual manipulatives http://nlvm.usu.edu/en/nav/vlibrary.html
links to activities http://rozauer.tripod.com/elemmath.htm
official site of Everyday Mathematics from the University of Chicago http://everydaymath.uchicago.edu/about/
interactive games http://resources.oswego.org/games/
interactive activities http://www.amblesideprimary.com/ambleweb/numeracy.htm
More math worksheets All skills and grade levels http://math.about.com/od/algebraworksheets/u/Worksheets.htm
Math problem solving contest http://mathcontest.olemiss.edu/