I've been pondering mixing a few horror genres: a serial killer who, after killing people, infects them with something that turns them into zombies. Or perhaps three witches who do a spell that turns people into werewolves. Love to hear some great ideas.
In my opinion the best horror stories are subtle and twist everyday occurrences into something that terrifies the reader. Take the 'Weeping Angles' from Doctor Who, for example. These statues appear normal and we see them every single day; we think little of them. But, what if there was more to them than meets the eye? What if, when a person blinks, or turns away, they move? What if, with every movement their expressions alter, and their bodies transform? It becomes a series of photographs - each more terrifying than the last. This is the sort of horror that will both excite and scare the reader... because it could easily happen to them.
'Blink' is my all-time favourite 'Doctor Who' episode for a reason. Well, it comes close with 'The Empty Child' - some very imaginative ideas in this show.
Why are the angles weeping? Are they too obtuse? Acute? As far as the mixing horror genres thing goes, I've made quite a few stories using this method. For example, I wrote a story about a girl who has dissociative identity disorder, and her other personality is downright evil. Terrifying enough on its own. Oh, by the way, did I mention that this person has superpowers and her other half destroyed the city of New York, killing millions, a few days ago when our protagonist lost control? Did I also forget to mention that our protagonist's final realization is that she's become weaker than her other personality, so the next time she relinquishes control, it'll be the last?
I can't watch episodes of Doctor Who that feature the Weeping Angels without wondering why people don't close one eye, open it, then repeat with the other.