So, I am already familiar with mobile devices and the fact that you can download apps to them. (I guess you could say my wow moment was back when I got an iphone a couple of months after they came out a couple of years ago). I think that the apps for teaching foreign languages or math concepts are great and could definitely be used in classrooms.
One app I found for iPad while searching around the app store in iTunes was on internet safety, called Professor Garfield Online Safety. Yes, as in Garfield the cat found in the comics. Its a humorous way to introduce safety concepts of being on the internet (there is another app by the same company but about cyberbullying, which also is a relevant topic). These might be too young for the high school set, but would be good tools nonetheless to teach students about being responsible when online.