Bookshelfporn is a site that posts just pictures of bookshelves.
For those interested in bookshelves from the historical and the engineering perspectives, I recommend: Petroski, Henry (1999) The Book on the Book Shelf. New York: Alfred A. Knopf. Not quite as good as his The Pencil. A History of Design and Circumstance (New York: Alfred Knopf, 1999), but still very good.
No further comment!