Here are some mathematical related websites:
http://www.funbrain.com/brain/MathBrain/MathBrain.html -Grades KG to 4th
http://www.primarygames.com/math.htm - Grades KG to 2nd
http://www.gamequarium.com/math.htm - Grades KG to 12th
http://www.coolmath4kids.com/ - Grades KG to 5th
http://www.mathplayground.com/games.html - Grades KG to 11th
http://www.multiplication.com/interactive_games.htm - Grades 3rd to 5th
http://www.oswego.org/ocsd-web/games/Mathmagician/cathymath.html - Grade KG to 4
http://www.gomath.com/game.html - Grades 6+
http://www.guidetoonlineschools.com/library/math-resources#basic - interactive math games and kid-focused math websites
http://www.apples4theteacher.com/math.html - Grades 1 to 4
http://www.k111.k12.il.us/King/math.htm - Grades KG to 10
http://www.cut-the-knot.org/games.shtml - Grades 1 to 11
http://www.math.com/students/puzzles/puzzleapps.html - Grades 1 to 11
http://www.bbc.co.uk/education/mathsfile/gameswheel.html - Grades 3 to 7
http://www.enchantedlearning.com/subjects/dinosaurs/activities/math-code/ - Grades KG to 1 (print and solve)
http://www.counton.org/games/ - Grades 1 to 12
http://www.eduplace.com/kids/mw/ - Grades KG to 6th
http://www.dositey.com/mathk2.htm - Grades KG to 4th
http://www.dositey.com/math58.htm - Grades 5th to 8th
http://www.prongo.com/games/ages9-12.html - Grades 3rd to 6th
http://hotmath.com/games.html - Grades 6+
www.gymnasiumforbrain.com -- all grades
http://www.teachertube.com/view_video.php?viewkey=93b89d8fbee5667d077f&page=1&viewtype=&category= -- grades 3+ (Math you SHOULD NOT DO!!!!)