I needed an insulated Arduino Bumper for a project at work. The bottom had to be covered to protect against shorting.
In addition to a covered bottom, I added a ridge at the top of the lip to hold the Arduino in and give you that satisfying "click" sound when you fully insert the Arduino. I also thickened the lip to make it a little more durable and lengthened the board a hair to compensate more for rough board edges. Finally, I enlarged the mounting holes slightly to make them clearance holes.
UPDATE 9/17/2012: I rebuilt the CAD drawing to clean it up and added some fillets for improved lip strength. Download the second file for this new and improved version.
This was derived from the Arduino Bumper by Chu.
UPDATE 7/3/2014 I redesigned this to eliminate the unnecessary plastic from the interior. Also, 3 simple cuts around the USB and power can modify this to work with the Arduino Ethernet.
Print, let bed cool down, carefully remove. Insert Arduino, ICSP connector end first. Carefully insert till you hear the click sound of the retaining lip grabbing hold.