DOOM!!

"Doom" or "Stoner" is a sub genre of metal that takes more of a Black Sabbath approach to songwriting. Thick walls of slow, heavy, fuzzy sludge replace the machine gun like attack of bands like Pantera and Slayer. Basically it's the heaviest blues you can imagine. Here is a list of doom bands that MUST be heard.

Sleep
Electric Wizard
High On Fire
Mastodon
Buzzov-en
Kyuss
Corrosion of Conformity
White Witch Canyon
Beehoover
Black Cobra
Clutch
Melvins
The Sword
Moss
Big Business
Roachpowder
Earth
Bongzilla
Weedeater

Here's a good place to start. Perfect Doom.