This is one of my absolute favorite books of all time, in any genre. It is the first book I give any of my friends who have baby girls (especially now that is available in convenient board book form). The best way to describe it is as a child's guide to individual thinking.
Elizabeth is a beautiful princess engaged to Prince Ronald, until a dragon destroys her castle and kidnaps her prince. Her kingdom in ruins and her prince gone, Elizabeth puts on a paper bag (the only thing she can find to wear) and sets after the dragon to rescue Ronald.
When she finds the dragon's lair she flatters him into showing off his fire breathing and fast flying, until all he can do is pass out from exhaustion.
Having defeated the dragon Elizabeth sets to rescuing Ronald, only to find Ronald is a snob and doesn't want anything to do with her: "Come back when you are dressed like a real princess."
Thankfully Elizabeth realizes that Ronald isn't the guy for her and decides she doesn't want to marry him, so she runs into the sunset on her own.
While most people view this as a book "for girls" I see it as a book for anyone. There is nothing wrong with teaching both girls and boys that a princess can just as easily rescue a prince. Rather than focus on the "feminism" of Elizabeth in the role of the prince or shining knight, I prefer to see it as the freedom to make your own decisions and being an individual. If the roles had been reversed and Elizabeth was rude to Ronald about not looking like a real prince I would hope that he'd have the same reaction that she did.
The best reaction I have heard from reading this book was when I sent my young cousin a copy and her parents read it to her and when it reached the end she said "That's it? No happily ever after?" Its better than happily ever after, its whatever Elizabeth wants it to be!