This book, by artist Tauba Auerbach, contains every color producible by combining red, green and blue. In theory, at least. I'm not sure whether it's strictly accurate. Still, it's an incredibly beautiful book, and I want one.
I've pretty much always believed that books are extraordinary items, but the categories of books that are extraordinary not for the stories in them but for the physical qualities of the books themselves is a lot bigger than I realized. There's the Google Dictionary, which, instead of definitions, contains the first Google image search result for every word. And there are books like House of Leaves, which requires the book's form to tell the story it contains.
I'm not any good at predicting the future, but my guess is that the transition towards ebooks and cheap publishing is going to free up a lot more space for a broader selection of kinds of art -- of books that depend more on their book-ness, and stories of broader selection and style.