I'm a big fan of the similar, but more philosophical, Sick of Beige cases that the Dangerous Prototypes folks came up with:

http://dangerousprototypes.com/docs/Sick_of_Beige_compatible...

They follow a standard size series, with standard mounting hole offsets, corner radii, etc. The idea being that if you're designing a PCB, you may as well go with one of these sizes because the laser cut cases are commercially available, or someone following the design can make their own easily too.

They work great with minimal modification for the Pi, Adafruit protoboards, etc.