Brain+Teasers

http://www.syvum.com/teasers/

http://www.braingle.com/Math.html

http://www.eduplace.com/kids/mhm/brain/gr2/index.html

http://www.eduplace.com/kids/mhm/brain/gr3/index.html

http://www.eduplace.com/kids/mhm/brain/gr4/index.html

http://www.eduplace.com/kids/mhm/brain/gr5/index.html

http://www.umassd.edu/mathcontest/brainold.cfm

http://www.umassd.edu/mathcontest/powold.cfm

http://www.mathcounts.org/webarticles/anmviewer.asp?a=142&z=7

http://www.eduplace.com/math/brain

http://www.nrich.maths.org/public/index.php

http://www.mathforum.org

http://www.educationworld.com/a_lesson/boxcars/boxcars004.shtml