Planet Waves Chordmaster
This is one of those items that at first may seem somewhat limited in it's use, but now I find myself using it regularly instead of trying to find chords in a book. It's a bit cumbersome to use because there are several menus to go through to select the type, variation, key, and position but there's also benefits if you are looking for a particular position of the chord on the guitar neck. I've come to depend on this gadget and I would not hesitate to replace it if it stopped working. Highly recommended.