I am just about finishing up with the following book: The Virgin Goddess: Studies in Pagan and Christian Roots of Mariology by Stephen Benko. Its a fairly dense academic book on the subject but, at this point, I'm heartily recommending it. Though there are some bits of theory I would quibble with (such as his rationalistic interpretations of the function of myth, and possibly inflating the roll of mystery religions amongst the common people of the time) it has been quite interesting in tracing pagan influences on the development of Mariology.
peace
-j
