the type geoffy explained can also be done by tapping with the right hand exactly on the fret that is 12 frets above the note fretted with the left hand. if u see what i meen.

when u tap, strike the fret and instantly remove the finger. takes a bit of pracitice to get them loud. but i find them less fidly than using the method geoff used. also if you tap with your second finger, like me, you will find that you can do this type of harmonic without dropping the pick.

incedentally if u use the pinch harmonic method i explained above exactly 12 frets above the freted note you get pretty much the same sound as if you use arch harmonics. but it does get harder with a fretboard in the way.