Mozart's requiem.....
I can listen to that over and over and over and over again....
as far as modern music goes there is numerous:
Godspeed you black emperor, Eluvium, Jesu, dark ambient examples tor lundvall, coil
eschatological music or neo folk: current 93, sol invictus etc etc
http://www.youtube.com/watch?v=OP2mpnBuZWI
there is of course neo classical genre...of whioch the Band Unto Ashes is a fave thsi band from New York City employed a classicaly trained Opera singer, violinists, hurdy gurdy etc etc...and drew references from modern paganism, death /black metal......and one to put Crowley's Hymn to Pan to music....
electronica... I particularly like the minimalistic output of bands like Pan Sonic...and of course Throbbing Gristle.