For some days ago I got The Hobbit: An Unexpected Journey - Official Movie Guide by Brian Sibley! I haven't finished reading it yet but from what I've read I can say that this is a really book! In September I bought another "Movie guide-thing" (which I think was more for children) and this one was waay better! It's approximately 170 pages and contains a looot of information about the characters, the actors, the production of the movie, the costume-making etc. I do really recommend this book althought it was (like many of these books) a bit expensive. I'm not sure if I would have bought it by my own (my mother gave it to me as a gift) because you had to pay ~ 300 kr here in Sweden (~ 28 GBP and 70 USD). However, abroad it might be cheaper. But if you want to buy one book about the movie, this is the book you should buy. Another thing which is a huge plus is the pictures in the book! I've never seen at least 40-50 % of the pictures which was really fun! (And the quality of the pictures is really good too!)
I just saw that Amazon is selling this book and it only cost 10.17 USD which is quite a lot cheaper than 28 GBP...