Looking for truly gory-won't sleep for a week-nailbiting scary authors?

right now i am reading richard laymon's books. i only have 2 more books to go and am looking for similar authors, if not scarier. i am not a fan of stephen king or dean koontz, so please do not suggest them. a friend told me that clive barker is very scary and gory. please give authors, and book titles if you can, but do not spoil the book!