Stephen King and James Herbert have been my favourite authors since I was young. First read the Rats when I was about 11 (good job books don't have pg and 18 ratings, hmm and I wonder why I have such a twisted and warped imagination).
Have also read a lot of Clive Barker, Peter Straub and most of Dean Koontz' books. Koontz is an excellent author, the Odd Thomas books are a superb read if you have not already read them.
As well as horror, I love fantasy and sci-fi, probably in that order after horror. Started with Robert E Howard and the Conan books after reading the comic books. Too many authors in the sci-fi and fantasy genres I like to list. The likes of Frank Herbert are worth a mention, particularlry for the Dune series. Plus the likes of Stephen Donaldson and Terry Pratchett obviously. George RR Martin is obviously popular at the moment because of the success of game of thrones. I'd read the orignal a while back, before the series came to TV, and the series has been a pretty good adaptation, but I hadn't gotten round to reading the others in the series. They have been sat on my shelves gathering dust.
I don't mind the odd thriller either. The Ninja series by Eric van Lustabder is excellent. It's not so much about martial arts, although there is an element, it's political intrigue, mystery, thriller with elements of martial arts and mysticism. He's also written fantasy but I've not read any of those so I may get around to that.
I have about 60 books I've bought over the past few years that I have not had time to read. My head has been buried in text books during that time. I'm looking forward to getting time to read them when I finish in June. It's going to be so nice to be able to take a good novel to the bog with me instead of some soporific science book. Even nicer to be able to read something and not have to try and remember all of it and take notes while I'm doing so.