"Nothing in religion makes sense except in the light of imagination." - me.
Phylogeny of major world religions. Just a draft, really -- I'm sure there are terrible errors. Religions from the East, from Africa, from Americas are much harder to find good information on. If anyone has good suggestions for revisions or additions, I'll replace the above with a more accurate, truthier version (see update below). If you've just started a new religion, send me your icon and I'll add it. I think a similar illustration (clearly not done by me!) should be the centerpiece of any and all books that attempt to summarize faith on earth.
For a good read on why religiosity might have been favored by natural selection (susceptibility to hypnotism!), get this: McClenon, J. 1997. Shamanic healing, human evolution, and the origin of religion. Journal for the Scientific Study of Religion 36:345-354.