This free online guitar lesson by Peter Vogl will teach you some basic music theory about guitar chords. There are four types of chords: major, minor, augmented and diminished. Every chord you will learn fits under one of those categories. This video will cover how to play an example of each for the A chord.
Watch the lesson: Quicktime or Flash
Here are the charts for the chords we will discuss in this video lesson:

Guitarist's Music Theory Book Digital Download by Peter Vogl is the first music theory course designed for guitarists by a guitarist. This downloadable .pdf explains music theory as it applies to the guitar and covers intervals, scales, chords, chord progressions, and the Nashville Number System. The .pdf features embedded .mp3 audio files that play all of the music in the book and also includes an ear training section. The Music Theory Book was written to help all guitar players achieve a better understanding of the guitar and of the music they play. View a sample page. $14.95