The heaviest song ever? Try anything from the band Sunn O))). I know lots of good heavy songs, mainly Death and Doom Metal ( Black isn't really heavy though it's equally extreme ). Doom is slower and darker and more atmospheric which adds to the heaviness factor, but Death is faster and more brutal. Good Doom metal bands: My Dying Bride, Shape of Despair, old Anathema, Swallow the Sun, Khanate ( extra heavy and weird ) Good Death metal bands: Nile, Hate Eternal, Incantation, Centurian, Vader Look around for an old thread called "metal" on the music forum with more Metal recommendations.
By the way, I've read a great description of the sound of Sunn O))), it was somewhere along the lines of "it sounds like a sunken battleship being raped by a gay drunk whale". So, yeah...
I played in a band who supported Anathema about 8 or 9 years ago (in Scotland)!!! (shit I sound like David Brent from The Office *reaches for the sleeping pills*) I always liked Testament for crunchy rhythms (Electric Crown!! Yee Ha!!). And lets not forget Slayer- At Dawn They Sleep, or Skeletons of Society.
We were called Incarnate. Didn't get signed, but played around Scotland for about 4 or 5 years. We played Progressive kinda thrash with Death Metal-ish vocals.
Yeah, try Black Sabbath - Into the void You're forgetting Cathedral, its the best doom metal band around. I also like Electric wizard and Acid king a lot. Old Anathema is also great.