Never been a huge fan. I've always felt they were a little overrated. I've got a couple of copies of their CD -- Back in Black and Dirty Deeds. I figure that gives me a copy of it with each singer. ;)

Three favs, I'd say:
Dirty Deeds
Hell's Bells
Highway to Hell or Have a Drink on Me, depending on my mood. I do love that opening lick of HaDoM.