Grades 7-12
http://cemc2.math.uwaterloo.ca/wired_math/index.html
http://chilimath.com/
http://jmathpage.com/middleschoolmath/middleschoolmath.html
These websites will reteach and give examples of problems that we discuss in class.
http://www.khanacademy.org/#arithmetic
https://www.teachingchannel.org/videos?page=1&categories=subjects_math,grades_6-8&load=1
Grades K-8
http://www.math-play.com/
http://hotmath.com/games.html
http://www.funbrain.com/brain/MathBrain/MathBrain.html
http://www.mathgametime.com/
http://www.ricksmath.com/count.html
http://www.figurethis.org/index.html
Grades Pre-School-3rd
http://www.teachrkids.com/