This interactive concept map, developed by Mark Morton in UW's Centre for Teaching Excellence, categorizes iPad apps into four kinds, and provides examples or recommendations for each kinds.
Learn how to develop you own iPhone and iPad app by downloading the "iPhone Application Development" course created by Stanford University. It's available on iTunes U.
A collection of interactive learning activities (interactivities) and simulations. If you try just one of them, check out the "Scale of the Universe" interactivity.