There are so many ways that students can get creative with ebooks that can be then published to iBooks on the iPad. We have touched on this in previous posts.
Creating your own iBooks
Creating iBooks or Ebook Apps
iBooks uses ePub format which is a free and open standard format created by the International Digital Publishing Forum (IDPF), designed for reflowable content that can be optimized to whatever device is being used to read a book file.
This post highlights some great resources for creating epub documents/books via Pages on a Mac or via devices/software other than on the iPad.
An excellent step by step pdf document 'Using iWork Pages 09 to create ePubfiles' from Charlene Chausis, Adlai E. Stevenson High School.
The ePub template that is recommended by Apple ePub Best Practices Sample Document.
A useful video tutorial on using Pages to create an ePub book:
ePub in Classroom