This is probably too expensive for most people ($145 USD), but maybe it's something to recommend for university or local libraries?

See:
http://www.amazon.com/New-Encyclopedia-Unbelief-Richard-Dawkins/dp/1591023912/ref=pd_bbs_sr_1?ie=UTF8&s=books&qid=1199899161&sr=8-1

Successor to the highly acclaimed Encyclopedia of Unbelief (1985), edited by the late Gordon Stein, the New Encyclopedia of Unbelief is a comprehensive reference work on the history, beliefs, and thinking of America's fastest growing minority: those who live without religion. All-new articles by the field's foremost scholars describe and explain every aspect of atheism, agnosticism, secular humanism, secularism, and religious skepticism. Topics include morality without religion, unbelief in the historicity of Jesus, critiques of intelligent design theory, unbelief and sexual values, and summaries of the state of unbelief around the world. More than 130 respected scholars and activists worldwide served on the editorial advisory board and over 100 authoritative contributors have written in excess of 500 entries.

In addition to covering developments since the publication of the original edition, the New Encyclopedia of Unbelief includes a larger number of biographical entries and much-expanded coverage of the linkages between unbelief and social reform movements of the 19th and 20th centuries, including the labor movement, woman suffrage, anarchism, sex radicalism, and second-wave feminism.

The distinguished contributors—philosophers, scientists, scholars, and Nobel Prize laureates—include Robert Alley, Joe Barnhart, David Berman, Sir Hermann Bondi, Vern L. Bullough, Noam Chomsky, Daniel Dennett, Paul Edwards, Barbara Ehrenreich, Antony Flew, Annie Laurie Gaylor, Peter Hare, Van Harvey, Susan Jacoby, Paul Kurtz, Richard Leakey, Gerd Lüdemann, Michael Martin, Martin E. Marty, Kai Nielsen, Steven Pinker, Robert M. Price, Richard Rorty, John R. Searle, Peter Singer, Ibn Warraq, Steven Weinberg, George A. Wells, David Tribe, Sherwin Wine, and many others.

With a foreword by evolutionary biologist and best-selling author Richard Dawkins, this unparalleled reference work provides comprehensive knowledge about unbelief in its many varieties and manifestations.