Joe Walnes made laser cut Raspberry Pi clips.
This one's for the Raspberry Pi hackers...
Adafruit (my heroes), make a really useful prototyping board for the Raspberry Pi - the Pi Plate Kit. http://adafruit.com/products/801
I love it, but I found one annoyance is that not all corners are supported - if you push down in the wrong place, it will bend the pins (see the clichéd style 'oh noes, look how bad it is' black and white photo).
This is a simple low cost solution that can be laser cut from acrylic plastic. It's just some clips (look at the blue supports in the corners).
You can download these from Thingiverse: http://www.thingiverse.com/thing:27209. The OpenSCAD source code is also available so you can modify the parameters to fit different boards.