Iron Maiden - Powerslave
I fully believe that this is the greatest heavy metal album ever recorded. It's as heavy as anything out there, riff and solo-driven, amazing vocals, amazing songs, amazing atmosphere...it just has everything. It's enough of the heavy metal sound from before and just enough of progression and memorable tricks to make it stand out. If someone asked me "What song best exemplifies heavy metal?" well...I'd show them Ace of Spades by Motorhead.
But after that, I'd pick any of the songs here. I don't know of any metal fan that doesn't know all the words to Aces High. Rime Of The Ancient Mariner is the definition of an epic in music and is coupled with the title track right before, which just so happens to be one of the greatest heavy metal songs ever written. It's just really hard to talk about individual songs on this album when they're all so fucking perfect. Needless to say, everyone needs this album. Twice.