I hate to come across as a lame fanboy, but my favorite guitar tone of all time is meshuggah-nothing (the original, not the remaster). Meshuggah has great tone after that album too, but somehow it isn't quite as compelling.
Other ones I like:
Darkthrone- Under a Funeral Moon, A Blaze in the Northern Sky
Metallica- Master of Puppets
Suffocation- anything
Death- Human, Symbolic
Burzum- Filosofem