I read Dan Burstein's 'Secrets of the Code' while I was on holiday. I would certainly recommend it as a companion to 'The Da Vinci Code'. I don't know whether others would agree, but I feel that it gives lots of information, without too much bias. There are areas where I think it hasn't made things fully clear - like the matter of the Priory of Sion - but I think it's well worth reading. There's a lot of food for thought in there.
You can find further details here:
‘Secrets of the Code: The Unauthorized Guide to the Mysteries Behind The Da Vinci Code’ by Dan Burstein‘This unprecedented volume provides a wealth of fresh insight from the world's most respected authorities on the novel's controversial historical, religious, artistic, and scientific themes. Interviews and commentary from renowned scientists, theologians, archeologists, philosophers, historians, and art historians ...’ http://www.amazon.com/exec/obidos/tg/detail/-/1593150229/002-8175887-1236053?v=glance ‘"After reading 11 debunker books, I consider Dan Burstein's Secrets of the Code to be the best of the lot," said Marcia Ford, FaithfulReader.com's reviewer. "Most of the other books I read were written from either a Catholic or evangelical Christian perspective; this one is a compilation of writings from people all along the DVC spectrum.’ https://secure.agoramedia.com/secrets/press_release3.asp
See also: https://secure.agoramedia.com/secrets/pop_press_angels.asp?promo=
Dan Burstein has an associated website, but you have to pay to join. There is a short free trial period, though. https://secure.agoramedia.com/secrets/index_secrets.asp
For 'faithfulreader.com', mentioned above, and its discussion on books about the Da Vinci Code, look here: http://www.faithfulreader.com/features/0405-da_vinci_debunkers.asp http://www.faithfulreader.com/features/0405davinci/davinci_code-authors.asp