Was given a couple of great books for my birthday in the Autumn. ABC3D by Marion Bataille is a fabulous alphabet in, well, 3D. Ingenious paper engineering and pop-ups of every sort. I tried taking pictures but this YouTube video of how the book works is much better.
The Art of Pop-up by Jean-Charles Trebbi is an excellent review of pop-ups and paper engineers from around the world. There's also a great timeline showing the history and development of pop-up books. A book to go back to time and time again.