Read all of Dan Brown and looking for more? Try these.
1. Cabal of the Westford Knight by David S. Brody
Did the Templar Knights ever reach the East Coast of the USA? A fictional but interesting action story, based on the findings of real artifacts and mysterious carvings found all over America. I call it "The Da Vinci Code for New England."
2. Steve Berry's "Cotton Malone series"
This series includes: The Templar Legacy, The Alexandria Link, The Venetian Betrayal, The Charlemagne Pursuit, The Paris Vendetta and The Emperor's Tomb (November). Cotton Malone, a bookstore owner in Denmark and a former US Justice operative, is always on the search for lost historical artifacts and treasures. With Steve Berry, you're sure to get a good dose of action combined with very interesting historical facts.
3. William Martin's Lost Constitution and City of Dreams
Peter Fallon, a Boston bookstore owner, brings the history of New England alive while chasing after historical documents that are either very important or valuable. Lots of local history and lots of action guaranteed.
4. William Dietrich's "Ethan Gage adventures"
This series includes: Napoleon's Pyramids, The Rosetta Key, and The Dakota Cipher. Ethan Gage is an American who some how ends up in Napoleon's army. Willy-nilly, Gage always gets involved in treasure hunts. Spectacular escapes, wild actions, history, and a lot of humor make those books very enjoyable.