The following books on creating pop-ups are great. I can recommend all of them!

The Elements of Pop Up, David Carter/James Diaz, 1999/Little Simon-Simon & Schuster

The Pop-Up Book, Paul Jackson, 1994/Lorenz Books

Pop-Up Paper Engineering, Paul Johnson, 1992/The Falmer Press

How to Make Pop-Ups, Joan Irvine, 1987/Morrow Junior Books

How to Make Super Pop-Ups, Joan Irvine, 1992/Beech Tree Books