We've been told that there will be an official case later on. For now, you can make your own -- it's part of the fun! There are some case designs at the Wiki: http://elinux.org/RPi_Cases.
At this point RasPi is a development board, not a complete system. One advantage to this is that RasPi can postpone EMI certification, and it was supposed to keep demand limited to developers so RasPi wouldn't have to deal with a crazed, media-enhanced stampede. Well, demand exceeded rational expectations, which is a good thing for RasPi in the long run :-)
You don't need a case. Freeze it into a block of liquid nitrogen, you be able to overclock if from its stock 700Mhz to 9Ghz... Whereupon, it will run windows 8 and play Cyrsis at maximum settings @ 500 FPS.
I am thinking a small pelican case - or maybe a large altoids tin to get my kids going! Heck, I have lots of other potential cases, just will wait and see!
