As a big horror film fan, I'm curious as to whether music alone is capable of creeping you out - to be able to switch the lights off, stick some headphones on, and listen to something that genuinely gives you the fear. I doubt it's something you could ever reach a consensus on, since music interpretation and the emotions it gives rise to is such a subjective thing; what might be scary to someone might be amusing for someone else. Personally, I find the genre that gets closest to having the fear factor is dark ambient - something like this for example:
Another one that spooks me out is Goblin's soundtrack for Suspiria - variations of the main theme can be heard throughout the film, but the scariest by far is when the music builds and builds to ear-splitting levels as the heroine is inching down the corridor past the crazy old woman and she can feel her projecting demonic vibes into her head - it's like a Velazquez painting come to life! That said though, divorced from the film, it loses some of its impact.
This one is more WTF than scary, but still freaks me out when listening to it in the dark:
If any fellow horror aficionados have any suggestions of scary music, I'd be interested to hear em!