Fantastic Beasts and Where to Find Them by J. K. Rowling

This and another book, Quidditch Through the Ages, are little-known (relative to the main series, of course) companion books to the Harry Potter universe.  Fantastic Beasts and Where to Find Them is a bestiary that describes in detail all of the beasts mentioned, and some of the ones not mentioned, in the Harry Potter universe.  This is also apparently a reproduction of Harry's own textbook, so it has graffiti in it from both Harry and Ron.  There is a forward by Albus Dumbledore as well.

One of the interesting things in the book is that the Acromantula, a giant spider, can achieve leg-spans of up to fifteen feet.  Now, most spiders have a small body compared to their legs, and the Acromantula in the movie was no exception.  However, no mention of magic was used to explain how a female can have up to 100 eggs in her body, and have each one the size of a beach ball without her exploding.  To say that she just stretches to accommodate the eggs would make her stretchier than a female termite.  Beach balls are big.  That many of them would make a female Acromantula far too large to do anything like, say, move.

Otherwise, I enjoyed the book.  I would have preferred a few more illustrations, but, like anything J. K. Rowling writes, it was fun for me to read.  Only read it if you've read the Harry Potter series, though.  Otherwise I would imagine it could get quite confusing.