The King who Rained
This is one of the more hilarious books that i've read recently. This is a book that teaches about Homophones and it illiterates what they are by saying one thing and drawing a different meaning for that word than what we normally associate with it.
I would use this book on higher grade levels, probably 5th or 6th and i would use it to demonstrate the differences between homophones and homonyms.
 - Fred Gwynne)