I guess I'll throw the obvious one out there: Stephen King.
Koontz has some good books, but he can be hit/miss. Mr. Murder is still one of my all-time favorites though.
I'll probably catch hell for this, but here you go:
Jude Devereax is another one of those mystery/romance writers like Nora Roberts. My wife read some book called "The Mulberry Tree". She liked it, and recommends it to you.