A post by +David Larkins over at the RPG Corner reminded me of the movie Eyes Wide Shut... and its soundtrack.
If you need music for a meeting of masked cultists performing some strange and terrifying ritual, then look no further than Jocelyn Pook's "Masked Ball." I love those Venetian Masks from the movie.
Grey Clouds--A Haunting Tune
The track most people recognize from the movie: Musica Ricercata, by Gyorgy Ligeti.
Other recommended songs on this soundtrack include:
Shostakovich: Suite #2 For Jazz Orchesta
Strangers in the Night
Get this Soundtrack if: You like running games that scare your players, you need music for a tense scene, or you like Eyes Wide Shut. You need background music for The Return to the Tomb of Horrors.
Don't get this Soundtrack if: You don't like the sound of monks singing backwards.