Map of dominant churches by county in the US.
Links to maps for each major religion - with Christianity broken down by denomination.
Interesting to me, at least. I grew up a Catholic (nominally, at least) in Tennessee. Recently we've started attending a Lutheran (ELCA) church in Minnesota. There's also a map of Religious Adherents which suggests how the coastal power brokers might have a little trouble understanding and relating to those of us in the fly-over states.