As far as something just fucking heavy that really hasn't been mentioned I think Crowbar's Time Heals Nothing is a fine example...just pure slow sludged out heavy metal.
There is a big difference between heavy and brutal. Death or thrash metal is not necesserarily heavy. For example; Reign In Blood isn't very heavy, but instead brutal. Heavy shit:
Black Sabbath
Candlemass
Cathedral
Neurosis
Cult Of Luna
Unearthly Trance
Trouble
St Vitus
Electric Wizard
Crowbar
Hatebreed
Yob
Khanate
My opinion of heavy may differ from others but here's some of my heaviest right off the top of my head:
Asphyx - The Rack
Obituary - The End Complete
Blood Red Throne - Affiliated With The Suffering
Napalm Death - Fear, Emptiness, Despair
Unleashed - Shadows In The Deep
Slayer - Reign In Blood
Nile - Amongst The Catacombs of Nephren-Ka
Fear Factory - Demanufacture
Hypocrisy - Abducted
Bolt Thrower - Honour Valour Pride
Carcass - Reek Of Putrification
The Crown - Deathrace King
Belphegor - Lucifer Incestus
You could even throw a little BM in here too:
Hecate Enthroned - Dark Requiems and Unsilent Massacre
Mystic Circle - Infernal Satanic Verses
Marduk - Panzer Division Marduk or Nightwing
Cradle Of Filth - Vempire or Dark Faerietales In Phallustein
There is a big difference between heavy and brutal. Death or thrash metal is not necesserarily heavy. For example; Reign In Blood isn't very heavy, but instead brutal. Heavy shit:
Black Sabbath
Candlemass
Cathedral
Neurosis
Cult Of Luna
Unearthly Trance
Trouble
St Vitus
Electric Wizard
Crowbar
Hatebreed
Yob
Khanate
What some people find heavy blows my mind. But I guess what makes something heavy to people is all diff and everyone is going to have opinions so fuck it.
There is no heavier. The riffs are crushing... absolutely no "subtle melody" to them, just pure madness. The vocals make them that much more insane. These albums ARE death to your ears... this is the definition of heavy. The only emotion seen here is anger...
I have that CD too. The thing is, some songs are heavier than others, since it is indeed basically a compilation of various material of theirs up to that point. IMO Left Hand Path and Clandestine are much heavier than any of their other albums.