Three favourites of mine spring to mind for you. i don't know if you've heard any of them as i have no idea what you're already into.
Im recommending these with the idea of it being stuff you havent heard before.
All three are very dark, alot of depth and alot of atmosphere. choose the right moment to listen to them.. you cant have them on in the background while you surf the net, it doesnt work. go to bed, switch off the lights, chill out.. then listen. listen in the order i post them..
Anoice - Remmings
This insrumental japanese band blend post-rock with a strong classical influence. This, their debut album, is a haunting masterpeice of beautiful classical musicianship with the atmosphere of bands such as godspeed.
Kayo Dot - Dousing Anemone With Copper Tongue
Again a strong classical influence, due to the multi-instrumentalist/lyricist/composer/vocalist and string musician/vocalsist duo, Toby Driver and Mia (who's surname i cant remember). Although there are about 10 people playing on this record, its all their work. Again its a blend of classical with a genre of modern rock, however this time it is doom... something (as far as i know) which had never really been done before, has been pulled off flawlessly on this record.
If you found Kayo Dot a bit too depressing/disturbing i do not recommend listening to number 3. not in the dark anyway.
Khanate - Things Viral
This is one of the most extreme, depressing, sickeningly dark yet brilliant records ive ever heard. this is the grim of all grimness (apart from one other album by one other band but i wont go into that here), yet worryingly their catchiest, most listenable release.
Well thats my intro to experimental doom.. i can give you some uplfting recommendations if you'd rather?