I just did a tutorial on chords specifically for acoustic guitar that covers mostly 3 finger chords and using open strings as well.
There's also quite a few 3 finger chords in the 'Minor 7' and 'Suspended Chords' tutorial as well.

http://www.guitartricks.com/lesson.php?input=9728&s_id=196
http://www.guitartricks.com/lesson.php?input=9750&s_id=199
http://www.guitartricks.com/lesson.php?input=9609&s_id=181

I'm also just working on a tutorial for alternate tunings as well that covers quite a few 3 finger chords for Open G and DADGAD tunings.
... should be finished later in the week.