My Sister in her Unitarian Church reading group (mostly members of the Pagan Caucus) read The Da Vinci Code. There are many books now to help decode The DaVinci Code. The one that looks the best (beside the one for $9.95 published by those neo-anarchists at Disinformation) is by Paul Burstein. Burstein, to readers of Max Elbaum's book on 70's and 80's USA maoism will recall that he was the editor of The Call, the newspaper of the M-L group led by red-diaper baby, Mike Klonsky, who interviewed leading cadre of the Khmer Rouge when Pol Pot was in power. These days Burstein helps to set up deals for US MNC's in the "PRC."
A week or two ago, Talk of the Nation on NPR had an hour on the Christian book market. One of the guests worked for a big secular mainstream publisher like Doubleday w/ a Christian book division. The Left Behind series (authors on the cover of Newsweek recently) sells overwhelmingly to Protestant fundies but a Catholic called in saying she was reading it too.