[zvinki]

How about Tool's last 3 CD's.

Aenema had a bunch of creepy images on the inside that, when placed under the serrated transparent plastic case, would render them 3-D.

Lateralus had a bunch of transparent images, created by Alex Grey, of a man. Each image focused on different systems of the body (circulatory, etc.) and you can place them on top of each other to get the complete man.

The latest, 10,000 Days, has 3-D glasses incorporated into the case that you can use to view the images on the inside.

Love 'em or hate em, you have to respect how much effort they put into their covers.