Since I keep seeing people on YouTube using crappy hacked-together RFID readers with Arduino, and I need easy RFID access in my new project, I decided to make a shield that takes an Innovations ID-12 or ID-20 RFID reader and hooks it right into the necessary pins on the Arduino. The shield fully open-source, and under a Creative Commons Attribution-Share Alike 3.0 license. The EAGLE files for the board are at http://www.liquidware.org/view.php?id=94
. Also at that link is a description of the circuit.
I'm sending the GERBER files for the board off to a board house next week.