Am I going to be the first to put up a link to classical music?Well, so be it...
I have always found that classical music can have a great power to creep. Stanley Kubrick believed so too, which is why he used it in so many of his films. Take Bartók's Music for Strings, Percussion and Celesta - which is one of my personal favourites. I first discovered this eery music when I was a teenager, it literally blew away my mind and started my love for 20th century classical. It's was used many times in The Shining, but most famously here:
It remains one of the pieces of music I find the creepiest to this day. I also find the simple tune composed by Ligeti in Eyes Wide Shut to be disturbing. It's amazing how just a few simple notes played on the piano can have such an effect.