I'm probably going for an old 3,5" HDD/5,25" optical drive enclosure I have lying around.
The built in power supply even supplies a 5v rail for the RaPi, and the aliminium look is pretty nice to the eyes too. Furthermore there's a on/off switch and a front LED. May also include a battery or two.
If I decide to try something besides this enclosure, it will be because of the size: The case is pretty big and heavy.