Since the initial release of the GB Pocket in 1996, Japanese corporations saw the system as a powerful advertising opportunity.  Many companies released limited edition systems as special promotions to attract business, and as a result, have become some of the biggest collectors items as far as video game systems go.
So take a gander at the product shots of these babies, because the screenshots are as close as you'll get to owning one (unless you live in Japan, or know someone in imports :)  ) with notable exception to the Ice-Blue and Extreme Green colors.

All Nippon Airlines: This GB Pocket was released in 1997 as a promotion for people who flew ANA for domestic (non-international) flights.
Atlas GB Pocket: This GB Pocket was released in conjunction with the release of a PC game of theirs from Japan.
Astro-Boy GB Light: Everybody's fave anime character is beautifully portrayed in this super-limited GB light model.
Imagineer GB Pocket This model was produced by imagineer, and given to people who bought imagineer products during a certain time period.  You could only get one if you won it.
Hello Kitty GB Light: Released to celebrate something to do with that cat that's on everything, this GB Light was packaged with a piece of Sanrio software.  Cute at the least.
Pikachu GB Light: Sold to commemerate the opening of Pokemon Centre in Tokyo, this was only available in Yellow.
Skeleton GB Pocket: I think this one was released from Famisu magaizine of Japan.  5000 of these were made, and they retailed for 7000 yen.
Tezuka GB Light: This one was released because.... I don't know why...  It's got some cool graphics on it though :)
Toyota GB Pocket The only gameboy you can drive.   Just kidding.  These were never sold, merely given away as promotional thingies.  I'd take one any day though!
Toys R Us GB Light: This is a GB light released in Japan, available at Toys R Us locations.  It's got a kinda interesting look to it, featuring that groovy green-esque casing, with the standard GB light hardware.  Feel free to buy one for me :)
Toys R' Us GB Pocket (JPN): These are like the above, sold at Toys R Us in Japan.  Nifty blue casing- once again- feel free to buy me one :)
Toys R Us GB Pocket (USA): Sold only at Toys R Us, this GBP features the same transluscent case, except in a bright green.  This was the only limited edition GB sold through the chain in North America.
Ice Blue GB Pocket: One of the few limited edition GB Pockets ever released in North America, this GBP features a matte-blue metalic finish.  Very nice.
Everything Else: Here's the rest of the limited edition GB pocket and GB lights (that I couldn't figure out where they were from).  They look oh so pretty no?