Eerie, Ethereal, Moody, Involving Soundtracks

One more.

"Remedies In Heresies" by Elijah's Mantle. This is music to accompany a film called "Philosophy With A Hammer". Too complex to explain musical character and context, but certainly non-secular, modern and majestically scary in old testiment kind of way. One of the CD label detail credits (photo) is called "The Damned In Hell"

DE NOVA DA CAPO DNDC 002 CD

Check out Broadcast. Theyre a band that makes music just like your describing. It sounds like everything is decaying beautifully.

I think you'll find the following fit your bill:

The Mission (Morricone)
La Otra Conquista/The Other Conquest (Zyman & Reyes)
Todo Sobre Mi Madre (Iglesias who scores for Almodovar)
Thin Red Line (Zimmer)

I'll second both "Blade Runner" and "The Mission" Will also add the soundtrack to "Baraka" and "Grand Canyon" and "More" (Pink Floyd)

OK, this may be more mainstream but the soundtrack to "Gladiator" certainly conveys loneliness and can be otherwordly at times. I like it anyway. If you like the Bladerunner ST you should check out some other works by Vangelis like "Opera Sauvage". Also, while not a soundtrack per se, the group Enigma's works have been used in many a theatrical trailer!