3. 'Iron Man'
You gotta feel bad for the "Iron Man" from Black Sabbath's 1970 classic. It's about a man who travels to the future and gets a firsthand look at the apocalypse. The process of traveling back turns him into an iron creature that is unable to communicate. Undaunted, he tries to warn everybody about the future, but nobody listens to him. (It's hard to blame them. Would you pay attention to some mute iron man wildly gesticulating as he attempts to warn you that mankind is doomed? They probably thought he was some crazy street performer.) So, Iron Man responds to this by going on a crazy, murderous rampage.
It's a wild story, but it hardly matters. The riff is one of the all-time greats. Beavis and Butt-Head even know it, and Ozzy has never been allowed offstage (solo or with Sabbath) without playing this song.