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.
This free eBook is available for download and provides a great interactive resources. Each section ties into some aspect of Bloom's Taxonomy and provides additional information to support iPad integration into the curriculum.
Touted as "the simplest way to make your own interactive eBook" this free program works on both Windows and Mac computers and is a great alternative to Apple's newly released iBooks Author.