I found an interesting website today while searching for some books. It's called Your Next Read. It easily finds books that you are looking for by typing in an author or title BUT...it takes it a step further. It takes the book you choose and it gives you a fun little map of other books that relate in some way to the book you picked. Here is a sample I ran for "Pete the Cat". Next to it are books that are related to it in some way.
I think this will help a lot when planning lessons and trying to find just the perfect book for a topic!