Oh, I had forgotten... Immortal, Celtic Forst, Burzum, Dimmu Borgir (OK, I don't like Dimmu Borgir, but well, they're heavy).

carcass, well they have the most disgusting song titles but i dunno if theyre the heaviest band ever, depends by what you mean "heavy"

First of all, I think Carcass are far from being the band with the most "disgusting" lyrics in the world and even if they have done some good stuff they are really far from being the heaviest band on earth. Don't you folks see how there is a difference in just playing fast and brutal with over distorted guitars and triggered drums. Black Sabbath sounded heavier in the 70's than any band has been able to sound even to this day. They don't need fancy production and shit like that. It's the spirit in their music, the riffs and the way they play their music that makes them the heaviest band on earth. Far more heavy than any death metal band, any black metal band or any thrash band (don't get me wrong, I like death, I like thrash and I like some black but it's not even close to being as heavy as Black Sabbath).
The only genre you should look at if you want a truly heavy band is doom metal and even in that name didn't exist when Black Sabbath started out they are still the godfathers of doom. And they are the heaviest band on earth.

Thats really hard to answer, because everyone is going to find something that they consider to be heavy in a different music genre.

Cannibal Corpse
Skinless
Parkway Drive
Gorerotted
Exhumed
Between the buried and me
Born from pain
Obituary
Caliban
Unearth
Bleeding through
Mortician- agreed even though i generally don't like that style of vocal
Disgorge
Maroon
The Red chord
Entombed
Dismember
Napalm death

Thanks for the list of bands, there are some that i am going to check out.

I'm gonna go with Job For A Cowboy. Definitely NOT Sabbath.

I'm more into Black Metal than Death Metal, really depends on what you mean by "heavy", but if you're looking for chaotic, fast and hateful bands, here's a few right off my head :

Infernal War (Poland) : http://www.myspace.com/iwofficial
Antaeus (France) : http://www.myspace.com/antaeusdpe
1349 (Norway) : http://www.myspace.com/1349official

If its the guitar riffs you're into, try out some Dragonforce

Daughters<3
The locust
The number twelve looks like you
Ion dissonance
Remembering Never
On broken wings
Bury your dead
The bled <3
Norma Jean<3
Nora
(Unearth and Bleeding through are amazing)
The devil wears prada
Converge!

I wouldn't call it 'black metal' or 'death metal' though.

but all awesome heavy/hardcore bands