Just take a look at all the books that were released shortly after The Da Vinci Code to cash in and you'll find a lot of similar ones! In all seriousness though, I actually enjoyed a book by John Case called The Genesis Code. The protagonist is a revenge driven ex-FBI guy called Joe Lassiter. The cause is the death of his sister and nephew at the hands of some religious nuts. Joe keeps digging until he discovers that the Vatican is somehow involved in the murders in an attempt to cover up something that they want to keep buried. It begins with Joe wanting to get revenge for the death of his sister, but spirals into a whole conspiracy theory that stretches across the globe. The Genesis Code is one of those kind of far fetched books that are nonetheless entertaining to read on a long flight, which is exactly how I would classify The Da Vinci Code.