The Kings and Queens of England by Nigel Cawthorne
My parents bought this book for me awhile ago, and I REALLY like it! I love studying about the Saxon kings, and I love both Queen Elizabeths, but it was also interesting to read about other monarchs that you don't hear about as much.
One thing, though: it's a more mature read (as in, teenaged + up... although I don't think anyone younger will be interested); the immorality of the monarchs + nobles is mentioned. Not inappropriate, just mature.
Anyways, if you love History, kings, queens, and England, go buy this book! :)