Ghasts are horrible, aren't they? All the creepy noises, and how they bury you in explosive fireballs the second you poke your head out of a portal? Besides drops, what possible good could they be?
Turns out they make a pretty good defense system! Check out this awesome video by Docm77 and ZipKrowd, which shows off the aptly named "Ghast Cannon Tower" in all its glory!