The University of North Texas has an excellent site on the History of Pop-Up Books, from the 1700's to today.

Meanwhile, Ann Montanaro's website also covers the Pop-Up history, and she also displays some of her excellent pop-up art.

Hawcock Books is a leading designer of Pop-Ups.

Finally, Joan Irvine, The Pop-Up Lady herself, describes and illustrates a how-to page.