The 500 Hats of Bartholomew Cubbins, by Dr. Seuss, Random Books, 1938.
Unlike most Dr. Seuss books, this one doesn't rhyme. And also unlike most Dr. Seuss books, this one has a hint of violence and a threat of danger -- a near-beheading of a child -- oh my! Maybe that is why this is one of my favorite Dr. Seuss books. Or maybe because it is shot through with fantasy and magic. Whatever the reason, this is a great book.