For me, always been Graham Masterton, and that's not just because he is Scottish.
He's managed to raise the hairs on the back of my neck on more than one occasion.
Interestingly, he used to be editor of Soft Porn Magazines Mayfair and Penthouse and has indeed written a few Sex Manuals.
Having said that, Sex is not splashed (get it) across every page of his books, although blood is.
I've never been disappointed by one of his novels and would recommend the "Night Warriors" series for those
curious enough to seek him out.