Higurashi Soundtracks -- While sitting alone in a dark room, use your phone or computer to search on youtube. Search for "Higurashi OST" and then you wait. This will creep the h*ll out of you. smile
Hetaoni -- Hetaoni OST's may not be horror-like, depends on which one you choose. Well, but they are still awesome.
Umineko OST -- If you wan't to feel like an magical, cruel witch, Umineko OST's is for you! Try inviting an friend you dislike to your house, and then turn on one of these, (Example: Black Liliana) and laugh like a phsycho! Works every time!
For feeling cute/girly:
Tokyo Mew Mew OST -- They are not awesome, but if you are an cute girl, you'll love these cute and pure soundtracks.
Feeling like on a adventure? Try the Twilight breaking dawn soundtracks! biggrin