Here at ReadItDaddy, now we're all e-book empowered, we love finding picture book ideas that cleverly use the functionality of the Kindle / iPad to good effect.
Charles and Rachael Vald's book "Clara's Ugly Monster" is a little treasure, using the touch screen of tablet devices to encourage children to delve into the book and find the 40 hidden sounds that are threaded throughout the story.
It's best demonstrated when handed over to the experts. Here's a great little video of Charlotte (Charles' daughter - not the 'blog boss') and her brother discovering the sounds for themselves:
You can find the book on iTunes here: Clara's Ugly Monster (Free Sample)
iTunes Full Version: Clara's Ugly Monster Enhanced Version (99p)
(It's also on the Kindle Store and available worldwide)