I recommend making a temporary (and free) subscription to the New Scientist magazine in order to read “The God issue“, which describes a range of interesting research efforts concerning religious belief.
Most interesting to me is the amalgamation of studies concerning children, and how their perception of the world primes them for religious belief. In a nutshell, religious belief is really a product of child-like thinking: of seeing agencies behind everything, and not just any agencies, but agencies with superpowers. This lends weight to the old, and rather creepy, Jesuit adage “Give me the child until he is seven, and I will show you the man”.
Also of interest is the idea that the evolution of religion might help to explain why hunter gatherers started forming larger social groups shortly before agriculture took off: they might have been getting together to perform religious ceremonies.