For more than a decade Black Sabbath, made up of Tommy Iommi, Geezer Butler, Ozzy Osbourne and Bill Ward, dominated heavy metal, selling close to 50 million albums. But in 1977 Ozzy went solo, recording Never Say Die before forming a band that would rival his first. But Black Sabbath carried on, helmed by Tommy Iommi and a succession of vocalists. Despite difficult times, these last two decades are now recognised as some of the finest moments in Sabbath's...