Kurt Vonnegut, Jr.: In an interview in Free Inquiry magazine he said his family has been "skeptical of organized religion" for at least four generations. In Palm Sunday (p. 210) he says "You have just heard an atheist thank God not once, but twice." He also calls himself a "Christ-worshipping agnostic" (p. 327). He is listed as Unitarian Universalist on the Famous Unitarian Universalists list from John Sias' 100 Questions That Non-Members Ask About Unitarian Universalism.
From: "Religious Affiliations of Celebrities" page in "Celebrity Religion" section of "Religion Facts" website (http://www.religionfacts.com/celebrities/religions_of_celebrities.htm; viewed 26 April 2007):
Below is an index of the religious affiliations or belief systems of celebrities (both living and dead; in film, television, music, literature, academics and politics), listed in alphabetical order by last name...
Celebrity: Kurt Vonnegut (b. 1922)
Religion/Belief: Atheism / Unitarianism
Quotes, More Information, Sources:
The American author has said, "I am an atheist (or at best a Unitarian who winds up in churches quite a lot)." - James A. Haught, 2,000 Years of Disbelief: Famous People with the Courage to Doubt (1996)