"War Pigs" is the best protest song ever, especially the parts starting at 3:20 and 6:07.
The opening riff of "War Pigs" is easily one of the most awesomely ominous E-chords ever strummed. It's not hard to imagine the apocalypse being ushered in by that note. It sounds just like THE BELL OF DOOM. And when the tempo changes, you know that this song is gonna be kickass!
Faith No More's cover is pretty damn good, too. As for Sabbath originals, there's "Die Young" or "Into the Void".
"Symptom of the Universe" is another biggie. It's a pile-driving number that helped inspire the thrash movement, but what really makes it awesome is that after completing the impressive main song, they float down with an effective acoustic coda.
If "Children of the Grave" doesn't have you headbanging by the first power-chord, you may not have a pulse. The opening instrumental "Embryo" should also get a mention for being so twisted and evil sounding. "Children of the Grave" has such a badass opening riff that it was used in the video games Brütal Legend and Guitar Hero: Warriors of Rock.
"Megalomania". The studio version is awesome enough, but this 1975 live version takes it to another level, especially after the 3:50 mark. Over the top of an absolute dinosaur of a riff, Ozzy jettisons actual singing for anguished shrieks, and sounds utterly possessed.
"The Wizard" is just bluesy enough to rock out, and just heavy enough to fist pump to. And it shows off Ozzy's harmonica abilities.
"N.I.B.", particularly the bass solo at the beginning. "OH YEAH!!!"
The title track from Heaven and Hell starts with a deep, pounding riff and beat, heavy and foreboding. Dio's vocals are a melodic wail, that complement the pounding rhythm, with a matching wailing guitar solo finishing it, only for halfway through to shift to an entirely-different-in-tone breakneck speed metal epic in its own right, completely with rapid fire lyrics. Almost sounds like entirely different songs, except the transition seems so natural, even inevitable, that the listener can't help but feel that the song becomes a whole entity, and incredible masterpiece. There's a reason the reunion of the Dio-led lineup took it as the band name for their tours and reunion album.
"Neon Knights" and "The Mob Rules" with Dio. If that doesn't get your blood pumping, you don't have any. "The Mob Rules" was used in a trailer to Brutal Legend. It will make you run with an axe too.
"The Writ", one of the few songs where the riffing takes a back seat to Ozzy's vocals.
"Children of the Sea" starts out pretty awesome to begin with. Then the chanting comes in behind one of Iommi's best solos and turns it epic.
"No Stranger to Love" off the 1986 album Seventh Star is a power ballad from Sabbath. That alone would have listeners bracing for the worst, but it is absolutely glorious and Glenn Hughes sings with such amazing passion and emotion.
"The Shining", a total gem from the Tony Martin era. Reeks of 1980's disease? Yes. Overly cheesy? Yes. But if the amazing riffs and extremely powerful chorus don't send a chill down your spine, you are a robot.