Number Sense Games
Addition:
http://www.ictgames.com/funkymum20.html
http://numbernut.com/basic/activities/add_series_2510.swf
Addition and Subtraction:
http://flash.hoodamath.com/numbereaters.swf
Subtraction:
http://www.sheppardsoftware.com/mathgames/fruitshoot/fruit_shoot_subtraction.swf
http://static.arcademics.com/games/mission.swf