The biggest influence on my life is the writing of William Faulkner. (I keep two paperbacks with me at all times. As I Lay Dying is one of them.) Perhaps it is the way Faulkner's 'common' man takes on a beauty and language all his own. Perhaps it is the complexity of sentence structure, or the contemplative nature of his characters. All I know is that -- without fail -- I cannot read one of Faulkner's novels without being driven to write. (with the possible exception being The Reivers, which doesn't satisfy, for some reason.)
Another write who sends me running to my computer is Annie Proulx. (Her Pulitzer Prize winning book, The Shipping News is the other paperback I carry with me.) In this case it seems to be her marvelous characterizations and bold sentence structure. My grandfather, who was a painter, always advised me to stop before I considered the painting completed. To let the mind of the observer finish it, while viewing it. This is how I feel when I read her work.
I seem to be driven to read certain books according to my state of mind. If I feel fevered, I pick up Andrea Barrett's The Voyage of the Narwhal and after a few minutes of reading, I sense an immersion into something wonderfully cool. If I'm bothered by life's complications, Thomas Pynchon's Mason & Dixon leads me to a place far more intricate. When my belief in human endurance wavers, McCourt's, Angela's Ashes, restores my soul.