Girl Start - this site has a wide variety of games and another things that appeal to young girls
Space Hopper Game - it gives you a picture of a constellation, see if you can guess which one it is
Proton Don - see if you can guess the symbols on the periodic table when the game gives you the name. Great practice for General Chemistry class!
Stay Afloat - this game is just like hangman, and you get to pick what subject to play