When I got my Pi, I did what any parent would do, and raided my daughters' Lego tub. Starting with the webpage of Biz's famous case on my laptop beside me (which soon got turned off due to rampaging kittens), I designed the case with access to all the ports and visibility for the blinkenlightzen. I think I did rather well:After building the prototype (and one-and-only production model), I stuck the design in Lego Digital Designer for some tweaks with the benefit of an infinite brick tub. I used the colours to highlight the layers. Note the use of flat plates to help support the PCB. The one below the micro USB power socket on the prototype is actually a Tyco Megabloks brick, which is slightly taller than a Lego flat plate. The layer of white plates below the roof may not be necessary when using the ideal bricks, as I put it there to help tie the bricks used on the prototype together.
Feel free to tweak and do what you will with it.
By the way, anyone know how to get a list of parts for Buy a Brick?