Be it the Ozzy or Dio years. Black Sabbath are one of the greatest bands of all time. Thank God (Or the Devil. You pick.) for Black Sabbath and Tony Iommi.
You've not heard their best, then. It's too late for me to actually pull up some Youtube links, but check out "Black Sabbath", "Sweet Leaf", "Heaven and Hell", "Mob Rules", and "War Pigs".