I wrote a tutorial on this subject called "Simple Harmonic Techniques" covering just about all the different types of harmonics.
You can read it here:

http://www.guitartricks.com/lesson.php?input=4227&s_id=35

If you need to hear the sound files, you'll have to register for the Highband membership here at Guitar Tricks, but hey, it's only $5 for access to about 3000 lessons so hey.