These are the works I relied on for the last essay, Morality Without God.
Richard Dawkins, The Selfish Gene, (Oxford, 1976, 1989). Dawkins gives some glimpses of the possible evolutionary origins of morality and also introduces the concept of memes.
Sigmund Freud, Civilization and its Discontents, (Norton, 1962), and The Future of an Illusion, (Norton 1975), both tr. James Strachey.
Jean Piaget, The Moral Judgment of the Child, (Free Press, 1965). Piaget observed children playing marbles and asked questions about the importance of the rules.
Robert Wright, The Moral Animal, (Pantheon, 1995). This is a popularization of Dawkins, Wilson et al. but a good place to start in thinking about the biological sources of morality. Most thought provoking but unpleasant line: "Like a lawyer, the human brain wants victory, not truth; and, like a lawyer, it is sometimes more admirable for skill than for virtue."
Edward O. Wilson, On Human Nature, (Harvard 1978). A short, interesting book by the dean of sociobiology. See especially the chapter on altruism.
Here are some sources on religion and atheism:
Interfaith texts contains materials on the major religions.
Brother Mark's Christian Material contains many links to other religious sources.
The Alt.Atheism Web represents the unbeliever's point of view, as does The Freethought Web
. The Internet Resources for Atheists page is also available.
The Religious Tolerance pages, hailing from Ontario, Canada, describe the salient features of the world's major religions.
You can search full text of the Bible at University of Virginia Bible Search.
Some sources on memes:
There is a Memetics home page.
The Memetic Lexicon is a glossary of memetic terms.
A page of links is the Alt.memetics Resource Page.
Charles Darwin's works are on-line. WWW Virtual Library: Evolution pulls together other evolution materials.