Back to Kubrick, he used Ligeti's Requiem in his movie 2001: A Space Odyssey. This haunting piece is perfect to set a darker mood for your erotica.
Sally's Song from A Nightmare Before Christmas is a haunting and sad tune that will bring tears to your eyes. So when your hero and heroine are far apart, this is the song to listen to that will gain you access to their hearts.
Lustmord was one of the first dark ambient artists I discovered over 20 years ago. The music is very atmospheric and perfect for setting a dangerous albeit sexy mood. Lustmord's Astronomicon sounds like something Emily Brontë or Daphne du Maurier would have liked. It has a Gothic and sensuous feel to it.
Now for something a bit more melodic. Enigma's The Principles of Lust is perfect for any sexy mood. You'll crack open the flavored lube listening to Enigma. You'll have to go to Youtube to watch and listen to this video.
Enigma's Sadeness (Marquis de Sade?) is another go-to piece. Here are parts 1 through 3. Same as above - you must watch and listen to this video on Youtube.
Now for something with a bit more bite to it. I can see listening to Lords of Acid while writing action-packed dark vampire erotica. Their album Voodoo U is especially sexy. Here's Special Moments.
How can you resist a song with a name like Dirty Willy, also by Lords of Acid.
Now that you're in a sinister but sexed up mood, grab a suitable book like Anne Rice's Sleeping Beauty trilogy or Poppy Z. Brite's Exquisite Corpse and give your dark side a treat.