The Da Vinci Code is currently being adapted into a film by Columbia Pictures, with director Ron Howard; the film will star Tom Hanks as Robert Langdon, Audrey Tautou as Sophie Neveu and Sir Ian McKellen as Leigh Teabing. It is scheduled for release on May 19, 2006.
Brown is working on a new novel, called The Solomon Key, which will reportedly take place in Washington DC, and feature the secret society of the Freemasons. Exact release date has not been announced, but the most common media speculation says late 2006 or sometime in 2007.
Brown's promotional website states that puzzles hidden in the bookjacket of The Da Vinci Code (including two referring to the Kryptos sculpture at CIA Headquarters in Langley, Virginia) give hints about the subject of the next novel.
Dan Brown says that he currently has outlines for at least 12 future books, one of which involves a famous composer's "all factual" associations with a secret society.
I am memeing this not because the article is interesting, but because the wording is. The last few paragraphs are *my* phrasing, lifted word for word out of the "Future Projects" section of the Dan Brown Wikipedia article, about 80% of which was written by me.