Some other Extreme acts that I listen to.

Children of Bodom - Something Wild, Hatebreeder, Follow the Reaper (awesome musicianship but lyrics are real crap, Power metal with harsh vocals)
Opeth - Blackwater Park, Deliverance, My Arms Your Hearse (One of the first of their kind, Extreme progressive metal)
Amon Amarth - Once Sent from a Golden Hall, Avenger, The Crusher, Versus the World (One of the good bands from Sweden. Have lived upto their expectations everytime, Viking-theme Melo-death metal)
Emperor - In the Nightside Eclipse, Anthems to the Welkin dusk, Prometheus-The discipline of fire and demise (One of the pioneers of Black metal)
Immortal - Pure Holocaust, Sons of Northern Darkness (Classic Black Metal)
Death - Human, Individual Thought Patterns, Symbolic (One the first Death Metal Bands after Possessed)
Atheist - Piece of Time, Unquestionable Presence (Progressive/Jazz death metal, an acquired taste)