It would be tough to narrow it down, but I would take a very logical approach to it. Giving up the entire reading world would be difficult for me, so I would have to pick an author that follows these three criteria:
#1. He/She wrote long books.
#2. He/She wrote MANY long books
#3. He/She wrote MANY long books that keep my attention and interest.
Jodi Picoult is up there, so is Stephen King (although, I'd be worried that my life will be filled with too many nightmares if I picked him heh), Judith McNaught (okay, okay, it's cheesy romance, but there are a lot of them, and they are all rather thick), maybe Shakespeare (I know he can be difficult to decipher, but I could get used to the language, and his stories are fascinating; also, they offer a nice variety: you get anything from comedy to tragedy).