Originally posted by Azrael
There is also a 4th type:

Tapping harmonics:

You have to be very fast for that one!
Finger a note somewhere on the fretboard and tap 12 frets above with yer index finger. But tap is exactly ON the fret - hammer the fret very hard and fast (tap it and immediately move the finger away again - like a woodpecker)

this will also cause a harmonic :)

-=[Azrael]=-