Integers
http://www.dositey.com/addsub/Mystery11.htm
http://www.funbrain.com/cgi-bin/osa.cgi?A1=s&A2=4
http://www.aplusmath.com/Flashcards/sub-nflash.html
http://www.cut-the-knot.org/SimpleGames/IntIter.shtml
http://www.mathleague.com/help/integers/integers.htm#positiveandnegativeintegers
http://www.aaamath.com/B/g65_cox1.htm
http://amby.com/educate/math/integer.html
http://www.mathwizz.com/integers/
http://www.math.com/school/subject1/lessons/S1U1L10GL.html
http://www.berghuis.co.nz/abiator/maths/sa/saintegercomparisons.html
http://www.berghuis.co.nz/abiator/maths/sa/saintegermultiply.html
http://www.berghuis.co.nz/abiator/maths/sa/saintegeradd3.html