Unless you've got kids, you probably haven't given a second thought to pop-up books since your own childhood. But really, they're one of the original forms of "interactive entertainment"--so it's no wonder that top-notch graphic designers have piled their talents into them. Here's three examples:

David Carter specializes just in pop-up books. His newest is 600 Black Spots, which is exactly what it sounds like---a compendium of 3-D graphic design, starring black spots throughout. Part of the fun is hunting for the spots

A bit more elegant, and a bit more modern, a pop-up calender by Johann Volkmer:

And finally, a recent classic by Marion Bataille, ABC3D, which caught fire on the Web and should make any type geek drool:

[Creative Review and Fubiz]