Gris Grimly (one of my favorite illustrators) decided to publish a book totally full of sketches he's made over a 13-year period. (Which 13-year period, I really don't know.) It's called Gris Grimly's Atrum Secretum: 13 Years of Hidden Truths, and will be available on Amazon October 1.
The book is beautiful, inspiring and discouraging all at once. Some of what he considers sketches I wouldn't be able to do on my best day. They make me want to do better at the same time they're punching me in the face and screaming there's really no hope.
Except for a title page, one end page explaining about the book, and copyright info just inside the end paper, the book is all about the sketches. The only text in the book was written when the sketches were drawn, so pages aren't filled with insight and analysis or whatever filler usually invades books like this.
I bought my copy directly from Gris, so mine is a little different than the one available on Amazon. (Mine looks like the one above.) In mine, he drew an original sketch on one of the pages before he sent it out (image to the right) and included a signed and numbered sketch coupon "certificate" to authenticate the drawing as original.