Here are two of my favourite education apps that are on my Ipod touch:
(1) ChemiCal: It a chemistry wonder it has: a periodic table with all of the parts, can figure out molar mass, dilution calculations, and it can find out the molarity of solutions. It can be useful in a chemistry class, but only if students can do the calculation on their own.
(2) Planets: Basically our galaxy in your pocket. It can tell you where each of the planets and starts are based on you location. It can be useful in any science classroom, more so in grade 9 science.