Chord spelling with what?!
If you ask most guitarists what the notes are in a particular chord, be prepared to wait a while as they form the chord on the instrument, figure out the name of the open string, count up the number of frets, calculate the note (probably missing some flats or sharps in the process) and give you the answer like this. D major = F# D A. While this answer is correct it has taken about 60 seconds to figure out, and the notes are not in root position (1 3 5).

When I studied at Musicians Institute we had a great teacher called Bruce Buckingham. He was (and still is) a wonderful player and had many short cuts in his arsenal. One of my favourites that I use every day in my teaching is CEGBDFACE. (Pronounced SEG BUD FACE ) This simple but brilliant little word is simply the music alphabet in 3rds. I have had students show this to their classroom music teachers and the teachers have been amazed at the simplicity of it.

No sharps or flats are in this, so of course we are dealing with the key of C. 

The idea with using CEGBDFACE is that it puts the notes in order and we can use the guitar (or knowledge of scales) to correct the required sharps or flats.

For example.. If we look at D major chord again. Start at D (in CEGBDFACE) and find the next 2 notes along. That would be D F A. This is not quite D major chord. The F needs to be made sharp. If a student knows their basic scales this should not be a problem. When we play the D chord on guitar and check it out carefully, the F# note appears.

If we think of CEGBDFACE as being in the key of C then all of the triads in that key will appear.

C major = C E G
Dminor = D F A 
Eminor = E G B
Fmajor = F A C
G major= G B D
A minor = A C E
Bdim = B D F

Pretty cool hey?
What about the 7th's? Again CEGBDFACE gives us the notes.

C major 7 = C E G B
Dminor 7  = D F A C
Eminor 7 = E G B D
Fmajor 7 = F A C E
G 7 = G B D F
A minor 7 = A C E G
Bmi7 b5 = B D F A

What about keys other than C?

Another way to approach CEGBDFACE is to change the appropriate note (s) in CEGBDFACE to match the key you are using. So, for G major the F note becomes F#. ( CEGBDF#ACE)  

G = G B D 
Am = A C E 
Bm = B D F#
C = C E G
D = D F# A
Em = E G B
F#dim = F# A C

This way of thinking speeds up the whole process and gets students in the 'ballpark' of the correct answer!