The Exploratorium now has two free apps for the iPad. The first one released is Color Uncovered and now Sound Uncovered. According to this post "both "buffet-style" collections of short, multi-sensory exhibits. You can select from a table of contents or swipe through like a magazine. The first was Color Uncovered, which uses properties of the tablet's display to demonstrate properties of light. The new app, Sound Uncovered, uses both the speakers and microphones, as well as text and video explanations, to show off some of the surprisingly bizarre properties of sound."

I have found many wonderful resources on the Exploratorium website, and suspect that both these apps would be great to have on iPads used in schools.