http://www.sheppardsoftware.com/mathgames/integers/FS_Integer_addition.htm
http://www.math-play.com/math-racing-subtracting-integers-game/math-racing-subtracting-integers.html
http://www.mathplayground.com/ASB_SpiderMatchIntegers.html
http://www.mathplayground.com/ASB_IntegerWarp.html
Integer Operations Quiz