The Documentary Hypothesis
Lane Core and Bill Cork have exchanged posts on the Documentary Hypothesis, a commonly-held theory among biblical scholars which posits multiple sources and editors for the first five books of the Bible: Genesis, Exodus, Leviticus, Numbers, and Deuteronomy. Lane's is here, Bill's reply is here (both of them focus on Genesis).
As Lane also mentions, there is an fun piece gaining attention in blogland, which "uses" historical-critical methodology to "prove" multiple authorship for the Pooh-Bear books. You can find it here.
For the record, I accept the validity of the historical-critical methods, provided that they're used in conjunction with other methods, and that there limitations are kept in mind by their practitioners.