CellCraft Biology Game
This activity was created by the folks at CellCraftGame.com, and made available to the public. Its great when talented people produce something with educational benefit, but its even better when they make it free to use.
Just go ahead and play (and learn!) You can't break it. The game leads you through an investigation of cell structure, function, and energy use. It is in .swf format, so you have to be using a browser with Flash capabilities (hear that, iPhone users?) If the music bothers you, notice that you have the ability to mute the sound at the bottom of the flash window.