Well I believe that some very important doom bands are:
Veni Domine - "Material Sanctuary"
Solitude Aeturnus - everything
Count Raven - "Storm Warning"
Candlemass of course - everything but their last 2
Last Chapter - "The living Waters"
Thunderstorm - "Sad Symphony"
Memory Garden - "Mirage", "Tides"
Memento Mori - "Life, Death and other morbid Tales"
(My beloved) Confessor - "Condemned"
Most of them are pure, slow, really heavy and in times epic doom metal followin mainly the Black Sabbath's "Heaven and Hell"/"Mob rules" and do not connect directly to the atmospheric doom/death that bands like My Dying Bride, Katatonia play.
I note this to guide your thoughts about the bands i mentioned above if you don't already know them.
I also should note that Confessor and Veni Domine have very strong influences of progressive metal.
Anyway on the other hand (thre atmospherodoomdeath) i will mention only one (not that i know many) album that really stuck in my mind and my heart. That is "OMNIO" by IN THE WOODS. I think you should really check it out...