If you decide you need even darker music than the already mentioned, you can check Portishead first two albums, Diamanda Galás (she is the queen of horror in her first albums), Nico's albums The Marble Index, Desertshore and The End. Then, as for boys, Coil are masters (were, they both passed away
) I suggest their last album, The Ape of Naples. Current 93 have many horror songs, but his albums Dog's Blood Rising and The Inmost Light are among the scariest stuff you'll ever hear
Enjoy!