I have so many art books laying around that it is ridiculous. So I will upload my 4 favorite ones for now.
First up...
Luis Royo was one of my FIRST all time favorite artists. (Along with Julie Bell) He used to do X-Men Fleer Ultra cards, and I have his Superheros and Heroins book around here too. (It was far too big for my scanner >_< ) Needless to say he and Bell fed my X-Men addiction for several years.
This particular book is hard covered and includes several hand written notes on what he was thinking while drawing. They are not clean sketches at all, you can see clearly where he moves limbs, and does several finished versions of the same idea until he finds one he likes.
Next...
But of course, right? I love this book. It is mainly manga scans (which I adore far beyond screen shots, although it has a few of those too) and at the back there are height charts and tid-bits of information.
I also have the Profiles book, but that book is more information filled than art filled. So I kinda clump them together.
And then...
Huge HUGE fan of Witchblade the comic. While this book does not show any progress sketches or anything like that, it DOES show a full character development, and offers a wide variety of different art styles for said character. It is always interesting to me to see how a character looks through someone else's point of view. It also includes the original art done by Mike Turner who sadly passed away just this past year from a long battle with cancer.
This book kind of opened me up to doing more... I dunno... organic things? Not everything is a clean line or makes perfect sense (as far as Turner's style goes) and it also is full of dramatic lighting and whatnot that I someday hope I can include in my own art work.
Finally...
This is quite possibly the most prized book I have. I have read this book cover to cover. I have learned that the characters are NOTHING like what they were originally sketched to be. The thought processes and the work processes are all included with this book ALONG with original art, screen shots and progress animation shots.
This book has held THE MOST valued information I have had as an artist/ creator. It has taught me that NOTHING NEEDS to be what it starts out to be, and if you let yourself wander in the land of possibility you will create something amazing.
That is more or less it. Like I said, I have a TON more art books, but I'd fill up an entire thread all on my own of it ^_^