Studying or practicing Ear Training?  If you're a musician, you should be.  You'll find my Palm software Ear Trainer invaluable.  Also, I teach guitar lessons in Orange County, CA.  (See OCGuitarLessons.com)

 
This is a good amount of chords to study, at least compared to the ten formations of the Triads:  34 essential formations (again highlighted in yellow).

If you're playing a six-string (or find the stretches inconvenient or too difficult), simply ignore the seventh string (and maybe even the sixth, too).  Usually, all of the essential pitches of these chords are represented in the first five strings.