Few days ago I found a really nice book for iPad programming :
iPad Programming: A Quick-Start Guide for iPhone Developers
I took it as eBook, there are some really interesting advanced samples that will help you to create reach human experience application.
Moreover, you can download all sample code explain on the book.
For more information go here : http://pragprog.com/titles/sfipad/ipad-programming
Unfortunately, this eBook is not free...