The heaviest band/album you've ever heard

I work on a seismic survey ship, and I'm concerned that blasting Electric Wizard out of the stereo system in the gym is going to interfere with the equipment being towed behind the boat.
Oh, and Crowbar too.
 
List yours here.

ok. my list:

Nightwish

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Evanescence

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Vanilla Ninja

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RBD

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1349

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Holy shit that is ... so fucking ridiculous.
It all depends on what your definition of heavy is. For me, for something to be heavy, it has to sound crushing, dark, and sinister. If by heavy you mean an extremely low end tone that makes the speakers buzz, then bluesy stuff can be heavy. That being said, I still don't think that Sabbath (or stuff heavily influenced by them) is heavy at all, though I obviously like and listen to Ozzy era Sabbath.
 
The original blues from long long ago were more depressive (after all, "feeling blue" means feeling down). But blues based rock is for the most party happy sounding. Just listen to hair metal or Led Zeppelin (the band that influenced hair metal).
 
The first thing that sounded fucking heavy to me was Sepultura's Arise, back in the day. It was awesome (and still is).

Guess the heaviest, most brutal stuff now is Anaal Nathrakh.