Gotta go with the series I'm reading now. First book is The Passage, and I'm halfway through the second, called The Twelve, by Justin Cronin. I love his writing style, and that it's an almost completely fresh premise for a story.
I've always enjoyed Tom Clancy, too, even if I don't agree with his politics. The Jack Ryan series is good, as well as Red Storm Rising, Rainbow Six, and Without Remorse, which tell stories of reoccurring characters from the main series. Everything after those are just kind of bad.
Robert Ludlum is good too, although I don't find his writing to be super compelling.