Black Metal.

Didn't Sunn O))) do a European tour where they played in a bunch of gothic cathedrals? Theres some videos on youtube. I don't really like their music, but I'd go anyway just for the awesome atmosphere.
 
I have been listening to Darkspace I and II for some months now. I really try to not overdo it and only listen one hour a week or so. I am slowly getting into it and I think this band will perhaps become one of my persoanl faves.

Darkspace are an excellent band with a great scope of sound. One of my personal favourites. There is a Darkspace III as well which is worth getting.
 
Didn't take time to read through the 501 pages of amazing, but here's a few that I'm into.

The Abyss
Ancient Rites
Arcturus (Not a huge fan of the more synth-y stuff, but they're amazing)
Aura Noir
Darkthrone
Emperor
Erasmus (My friend's band, check them out)
Marduk
Nifelheim
Pagan Hellfire
Primordial
Galar
Tulus
Unlord
Vindland
Watain

To name a couple.
 
"The Diabolical Serenades" is essential black metal. Easily one of my favorite albums. Ophthalamia's "Dominion" is another (don't know how I forgot them).

edit: Your band sounds really good, too. I dig the vibe.