Haruki Murakami is the only living author who, if he writes a book, I will read it. The only other author for me in this category is C.S. Lewis (except that he's not still living in this world).

Also, I would have answered the question with "Hardboiled Wonderland and The End of the World", except that, by the time I read it, I was already so much on the same page in my thinking, that it didn't have a huge impact on me... but if I hadn't already been thinking as I do, I'm sure it would have been immensely impactful.