This is a great article from UX Magazine. It does a great job defining interactivity and gives video examples of eBooks and eBook apps that have value.
Lately, we have been discussing using QR Codes to help manage workflow for disseminating content to be accessed on iPads. This is another great post from Richard Byrne, with an embedded Common Craft video, explaining ideas for QR Codes in the classroom.
Vernier offers a host of products to support physics instruction, and for $2.99 there is now an app. Students can perform hands-on experiments and collect real-time data through the iPad.
This is a free app that is similar to iMovie. For an additional $.99, you can have full capabilities of adding photos, music, voice over, and transitions.
This site offers tools for studying vocabulary. There is also a selection of apps available. What makes this interesting for students is the visuals provided by both images as well as video to give additional cues for learning words.
This is an interesting app that seems to be a cross between Fotobabble and Animoto. The idea is that you can record ambient sound while taking pictures in order to create a short video. Could be an interesting way to document field trips or create a digital story.