Here are some of my favorites:
"If the book is good, is about something that you know, and is truly written, and reading it over you see that this is so, you can let the boys yip and the noise will have that pleasant sound coyotes make on a very cold night when they are out in the snow and you are in your own cabin that you have built or paid for with your work." ~ Ernest Hemingway
"The artist, like the God of the creation, remains within or behind or beyond or above his handiwork, invisible, refined out of existence, indifferent, paring his fingernails." ~ James Joyce
"A serious writer would gladly swap 100 readers now for 10 readers in 10 years or one reader in 100 years." ~ Flannery O'Connor
"If my doctor told me I had only six minutes to live, I wouldn't brood. I'd type a little faster." ~ Isaac Asimov
"Fiction is the truth inside the lie." ~ Stephen King
"Writing ought either to be the manufacture of stories for which there is a market demand -- a business as safe and commendable as making soap or breakfast foods -- or it should be an art, which is always a search for something for which there is no market demand, something new and untried, where the values are intrinsic and have nothing to do with standardized values." ~ Willa Cather