Originally Posted by: 6strngs_2hmbkrswell, if you know your intervals, then it's pretty simple. (let's just hope I remember this right)
Major chord = Major 3rd + minor 3rd
minor chord = minor 3rd + Major 3rd
diminished chord = minor 3rd + minor 3rd
augmented chord = Major 3rd + Major 3rd

with a minor third being 3 half steps(1 1/2 whole), and a major third being 4 half steps (2 whole).

examples:
C Major chord = C (root) - E (Major 3rd) - G (minor 3rd)
C Minor chord = C (root) - Eb (minor 3rd) - G (Major 3rd)
Cdim Chord = C (root) - Eb (minor 3rd) - Gb (minor 3rd)
Caug Chord = C (root) - E (Major 3rd) - G# (Major 3rd)

and so on, and so forth. of course, I don't know if I used #'s where they were appropriate, and b's where they were appropriate.. I tried.. but I still don't understand the rules fully myself :p