I was surprised to see that Earth hasn't really been mentioned here, and, although Dylan Carlson has never been a strict Sunn devotee, he has and continues to use Sunn amps to beautiful and deafening effect. After all, the their 1st live album is titled "Sunn Amps and Smashed Guitars." Still, in addition to the mighty Model T, I've seen Dylan using dual Marshall stacks, Ampeg V4's, and Silverface Fender Bassmans.
Starting in 1990 with the Sub-Pop released "Extra Capsular Extraction" and continuing with the landmark "Earth 2," Carlson and Co. arguably launched the modern drone movement. More structured and "musical" than later drone efforts by bands such as Boris and SunnO))), Earth--in my opinion--offered the most thoughtful and well-crafted drone until SunnO)))'s most recent album, "Monoliths and Dimensions."
In recent years, Earth have focused more on clean tones and soundscapes, but I'll always prefer their earlier efforts. If you're into this sort of thing and don't already have Earth's back catalog, I highly recommend buying it. If you can't afford it, drop me a line, and I'll make sure you get copies.
Cheers,
James