iBook Skin
A few years ago I followed the instructions on Applefritter and removed all of the white paint from the inside of my old iBook. I replaced it with a map of France from an old Michelin altas.
UPDATE Thanks to everyone for the response. I've posted a few more images of the iBook here since the ones above aren't that great. I also wanted to note that Apple has changed the way they manufacture iBooks so that they no longer have a transparent shell (probably due to the extra cost and higher failure rate of painted clear plastic). That means this kind of modification isn't possible on any recent version, but there are some companies that sell iBook "skins" or re-colored iBooks.
Other Ideas
I like the map, but thought I could make it into something a little more interesting. A few ideas are below, click on the image for a large version. If you have any concepts you want to try, here's the PhotoShop file I was using: 8.9mb zip.
A Paul Smith-style ibook, complete with stripes.
SkyBook
Pretty Colors
White Stripes. The area between the stripes is left transparent.
Little Black Book. This might not work since parts of the plastic are a bit frosted (I'm not exactly sure why).
Blue Book
Buildings.
Sidewalk.
Glow. Anyone know where to get glow-in-the-dark spraypaint?
Inverse. Of course, I'd have to set my desktop picture to an image of the back of the screen.
More stipes. This time created by wrapping the pixels from the edge of a photograph.
Camoflauge. Good for hiding from the conductors on the train.