A freethinker is one who forms opinions on the basis of reason,
independently of religions or other authorities.

links:

http://nobeliefs.com/freethinkers.htm
http://www.infidels.org/library/historical/joseph_mccabe/dictionary.htm
Thomas Paine's Age of Reason Part I: http://www.thomaspaine.org/Archives/AOR1.html
Age of Reason Part II http://www.thomaspaine.org/Archives/AOR2.html
Works of Robert G. Ingersoll http://www.infidels.org/library/historical/robert_ingersoll/
The Center for Inquiry: http://www.cfiwest.org/index.html