An author that you will read whatever they put out.
That's a tough question. There are a couple that I would probably read no matter what. J.K. Rowling, Jean M. Auel, Charlaine Harris, probably even Stephenie Meyer because I enjoyed The Host so much. There is probably a few more as well.
There are a few that come to mind, but first in line is definitely Stephen King, I always anxiously await every one of his books and usually own it within a few days of it being released. Other authors I would place in this category would be JRR Tolkien, Charlaine Harris, George RR Martin, and JK Rowling. I'm sure there's more, but those are the first that come to mind :)