"My adventures as an illustrator by Norman Rockwell"
This is a great read. He tells the story of his life from when he was a boy around the turn of the century on up until the late 60's early 70's. His son, Tom Rockwell, finishes NR's last years of the book up to his death in the late 70's filling in where the original printing left off. It's not so much an "art book" with a collection of his works as it is the story of his life and his art combined. You will gain a whole new appreciation of him as well as for illustration. There are some great images throughout, and you see his progression in chronological form. But the real meat is in his storytelling. I highly recommend it.
Another notable book from me, from an artist based in the comics field is "The Art of Brian Bolland". I just recently got this for Xmas, I haven't read anything thoroughly yet, but the artwok in it is spectacular. It spans his entire career from the 60's to the present. It's a huge book, 300+ oversized pages. If your a comics fan, or a fan of incredible draughtsmanship it's a prize of a book.
I have a few more recommendations, but I thought I'd pipe in with these for now from 2 very different illustrators.