The Rules: Don't take too long to think about it. Fifteen authors (poets included) who've influenced you and that will always stick with you. List the first fifteen you can recall in no more than fifteen minutes.
In no particular order:
T.S. Eliot -- The Wasteland has a special place in my heart. My dry, black, bitter heart.
Robert Heinlein -- Can't say I like his stuff so much anymore, but it was certainly influential.
Theodore Geisel (Dr. Seuss)
Lois McMaster Bujold
Stephen Jay Gould
Steven Brust -- Not so much influence, I don't think, but a memorable body of work.
John M. Ford
Ursula K. LeGuin
Sherri Tepper -- I don't like her work that much, but I find it interesting.
Stephen King -- Umney's Last Case
(The "influential" part means this is biased towards authors I encountered fairly young, so there's been time to be influenced. Authors I've read more recently who will belong on this list in a few years when their work's had time to marinate include Peter Watts, Pamela Dean, and Jo Walton.)