Ponoko is one of our favorite websites. Need a 2d or 3d item made for you? Don’t have a machine shop? Design a gear, or case, or whatever, in Inkscape, Google Sketchup, etc., upload it to Ponoko, and they will ship it to you, or even list it for sale on their website.
One of our favorite items is a Arduino mounting board, to keep our Arduino and a breadboard stable while we experiment.