All the authors I would have mentioned are already here, also consider Robin Cook - some good medical stuff. Its not horror horror, but its mostly medical horror/mystery-horror stuff. Just to reitterate:
Clive Barker - weird, strange, mystifying and sometimes scary? yea I guess
Anne Rice - not scary and probably not considered horror, just good reading (the original 5 vampire chronicles any way)
John Saul - cool, interesting, but again - not really scary
But then again I don't get scarred by anything anymore, this is a result of reading Stephen King at the age of 9-10.