Pain Of Salvation, absolutely
Porcupine Tree
Mr. Bungle
Maudlin Of The Well/Kayo Dot
Naked City
Univers Zero
Devil Doll
Enslaved
Moonsorrow
Deathspell Omega
Weakling
Katatonia
Esoteric
Skepticism
Devin Townsend Band
Elend
Dead Can Dance
Neurosis
Isis
Godspeed You Black Emperor
Explosions In The Sky
Sigur Ros
Red House Painters
Meshuggah
Most things Dan Swano did
Anglagard
Ayreon
...if we stick to only bands. I've got a whole other list for dark ambient/industrial/classical composers. Opeth is great, but they aren't even close to covering all the ground needed to be the "best". No band is.