[Sircastor] a.k.a. AaronEchie shared a nice link on the Arduino Forum, a step by step guide to skecth (and possibly send to production) a PCB shield for your Aruino using CadSoft’s EAGLE program and SparkFun EAGLE library.
So you’re pretty fond of your Arduino. You make blinking lights, and beeping noises. You’ve made a robot that was pretty cool. Or maybe you didn’t. Who cares, You’re ready for the next step. You want to extend it. Although you can just plug in wires, there’s something very appealing about making a shield. Instead of a rats-nest of wires piled about and plugged into your prototyping breadboard, you can have a nice clean shield with labeled connections and a smaller footprint. So here I’m going to tell you everything you need to know to make a schematic and PCB layout, and get a beautiful shield that will plug into the top of your Arduino.
more on [aaroneiche]