9. Paranoid - Black Sabbath
Half of the roots of Black Sabbath tend to go back to the blues. Despite Tony Iommi's penchant for writing guitar riffs that could scare you half to death, all of the songs on their first handful of albums tend to have one foot trailing back into the same 12 bar exercises, with some songs even sounding like Cream in some spots. The blues often leads to jams though, and there's only so many of those you can put on a record.
When Sabbath were making the first steps for their second album, the songs began to stretch out for much longer than any traditional single, with classics like War Pigs and Iron Man going well over the 6 minute mark. Once they came up for air though, they still needed a few more minutes on the vinyl to help pad out the runtime, and they figured they would just jam something in the studio to act as a bit of an interlude.
What came out instead was one of Tony Iommi's greatest riffs, having the same kind of bluesy feel with the power of Godzilla behind it, as the rest of the band rushed to their instruments trying to figure out where they fit. It may seem like the most natural thing in the world when you hear it on the record, but when they were in that room on the last days of recording, you just had to make sure that you kept up with Tony wherever he went.