I'd say that Cowboys From Hell by metal gods Pantera is the kind of all metal tracks. If you had to bottle everything that's awesome about heavy metal, you'd be left with Cowboys From Hell.
Next up, Painkiller (and indeed the whole of the similarly titled album) by Judas Priest is just a masterwork of metalnessness.
I send much love and respect Nouw for suggesting Megadeth, even if he did suggest the wrong song. Rust In Peace (Polaris) is what he was looking for.
I'm not really keen on anyone suggesting things that were released after about 1990 unless it's from a really established band who kept being metal throughout. There's some good bands around today, but unless you were around when heavy metal was still developing, then you don't count in my book, particularly when you are talking about something being a masterpiece. Masterpieces are what initially built and solidified a genre. Once the rules are there, anyone can follow them and make something great, but its not a genuine masterpiece. Anyone can paint like Picasso, but only his work is a masterpiece.
Oh and Rammstein aren't heavy metal. Sorry, they just aren't. They are a great band, but the are definitively not a heavy metal band. They are part of Neue Deutsche Härte, which is itself an offshoot of Industrial. There's a HUGE raft of music that could be vaguely considered heavy metal because it has distorted guitars, but that's just not enough. Only original heavy metal (priest and maiden) and its immediate family (speed, thrash and glam) really come under the umberella. You can maybe nudge in doom and death metal if you really must, but the more modern hybrids aren't the same thing at all. I really don't wanna be 'that guy', because I hate that guy, but it needs to be said.
