Green Zone - for some reason I really like Paul Greengrass. He took a solid action base, The Bourne movies, and transferred that style into a cerebral thriller. Though it's hard to call it a thriller as it's fairly obvious going into the film that government members will be shady characters and Damon will try to thwart them. I don't think that takes away from the movie at all. That said, Green Zone isn't better than the Bourne films or worse, it' a start to finish solid film.
Syriana is definitely the leader for these types of films. Realistic fiction, based loosely on real people and real events that causes the viewer to think and question.