contributor

from The Century Dictionary.

• noun One who contributes; one who gives or pays money or anything else of value to a common stock or fund; one who aids in effecting a common purpose; specifically, one who furnishes literary material to a journal or magazine, or other joint literary work.
• noun 2. One who pays tribute; a tributary.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who, or that which, contributes

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A benefactor; someone who donates to charity or some cause.
• noun A person who backs, supports or champions a cause, activity or institution.
• noun A person instrumental in the creation or growth of something.
• noun A person who produces articles published in a newspaper, magazine, online publication, etc.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun someone who contributes (or promises to contribute) a sum of money
• noun a writer whose work is published in a newspaper or magazine or as part of a book