Great for creating graphs for science or math. http://nces.ed.gov/nceskids/createagraph/
National Geographic for Kids http://www.nationalgeographic.com/kids/
Math - LCM http://www.mathgoodies.com/lessons/vol3/lcm.html
Math - Multiplication Mystery http://www.harcourtschool.com/activity/mult/mult.html
Math Grid Game http://www.bbc.co.uk/education/mathsfile/shockwave/games/gridgame.html
Factor Game http://illuminations.nctm.org/ActivityDetail.aspx?ID=12
Factor Trees http://nlvm.usu.edu/en/nav/frames_asid_202_g_3_t_1.html
Aleks http://www.aleks.com
Make your own Rock Candy at home! http://www.youtube.com/watch?v=WQdXbf8huuQ
Sales Tax math game http://www.math-play.com/Sales-Tax/Sales-Tax.html
Penguin waiter percent game http://www.funbrain.com/penguin/
Fraction and percent matching game http://www.mathplayground.com/matching_fraction_percent.html
Percent Shopping http://www.mathplayground.com/percent_shopping.html