I would start with Angels and Demons. I think it's better than Da Vinci Code, and it comes before Da Vinci Code so you get to know the characters better that way. Digital Fortress and Deception Point are not nearly as good, but still decent.
If you like action books, I would recommend Matthew Reily (Ice Station, Temple). They basically read like an blockbuster action movie. Clive Cussler is another good author along those lines, but I find his books much more hit or miss - some are great, some suck.