I'm almost done reading the book In Gods We Trust: The Evolutionary Landscape of Religion by Scott Atran. This is a much better book than A Theory of Religion (read: religion via rational choice) or Darwin's Cathedral: Evolution, Religion, and the Nature of Society (read: religion via functionalism & "group selection"). I would caution that it is somewhat dense & technical, though I don't think it will deter a determined lay person too much (I am a newcomer to cognitive science & psychology). I will offer my thoughts on Atran's book later, but I wanted to plug it here so that some readers will go out and read it, it's really an incredible work as far as I'm concerned.