This web site is one of my favorites! http://www.iknowthat.com/com/GradeLevel?GradeLevel=3&Subject=All
http://www.aplusmath.com/
http://www.coolmath.com/
http://www.mathstories.com/
http://www.math.com/
http://www.funbrain.com/math/
http://www.mathgoodies.com/
http://www.eduplace.com/math/brain/index.html
http://www.figurethis.org/index.html
http://school.discovery.com/brainboosters/
http://mathforum.org/library/drmath/sets/elem_puzzles.html
Great site to practice "Rounding" http://www.321know.com/est28bx2.htm
Site for measuring perimeter and area. http://www.mathplayground.com/area_perimeter.html
http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks2/maths/perimeter_and_area/index.html
Websites for learning about Fractions. http://www.visualfractions.com/Games.htm
http://classroom.jc-schools.net/basic/math-fract.html
http://funschool.kaboose.com/formula-fusion/number-fun/games/game_action_fraction.html
http://math.rice.edu/~lanius/fractions/index.html
http://www.internet4classrooms.com/skills_3rd_original.htm