It doesn't seem to be generally recognized, but The Da Vinci Code by Dan Brown is in fact the second novel to be largely inspired by Holy Blood, Holy Grail by Michael Baigent, Richard Leigh and Henry Lincoln. The first, as RAW fans will know, is The Widow's Son.
Without giving too much of the plot away for people who have not read the book yet, the Merovingian bloodline and the mythology of the Holy Grail play a large part in The Widow's Son. I looked through The Widow's Son after I finished reading it Sunday, and there are references to Holy Blood, Holy Grail in 11 different footnotes. In some of those footnotes, Holy Blood is cited more than one time.
Considering the amount of attention that The Da Vinci Code attracted, it seems odd that so few people have noticed that it is actually the second work of fiction to draw inspiration from Holy Blood, Holy Grail. The Wikipedia article does not even mention The Widow's Son. Perhaps this was a missed opportunity for Wilson?