Book Writer is a great iPad app that can help students creating digital books.  Students can add video, images, music, and record their own voices to narrate.  One nice thing about Book Writer is that you can export the books to iBooks, share them by email and print from a PDF.  Book Writer is currently $3.99 in the Apple app store and I encourage you to check it out at any grade level.  The embedded video below will give you more of an idea about this app.