Check out at this awesome video about pop-up books. 20,000 Leagues Under the Sea looks terrific.
Our family's favourite pop-up book (hands down) is Star Wars: A Pop-Up Guide to the Galaxy. The book is a mind boggling feat of paper engineering. We also like Artist to Artist: 23 Major Illustrators Talk to Children About Their Art. I find it totally fascinating to learn how illustrators (and paper engineers) engage in their craft.