Diet -- anything that keeps your blood sugar stable and on an even keel. When I first started jitz I had some cheese around the middle from being on prednisone. I wanted to get rid of that and drop to 170 or so for competition. I basically just did your generic low-carb/high protein diet for six weeks and dropped 19lbs; the vast majority from around the middle. I went from a 36 to a 32 and have stayed there for three years. I have a hard time with that diet now because I can't handle fiber very well and eating fiber + fat is right up there with eating broken glass and gasoline.
Exercise -- anything that uses large muscle groups. There are several exercises that have been shown to improve your abdominal circumference and the thing they all have in common is that they use as many large muscle groups at a time as possible. This pretty much means core + legs; so burpees, bear crawls, squats, deadlifts, box jumps, etc are all good. I've become a recent convert to Tabata interval training. I don't know that Tabatas have been shown to improve belly fat, but they do substantially improve your cardiovascular conditioning - moreso than moderate distance running. It seems to make theoretical sense at least that if you are doing large-group exercises in a Tabata format you should see improvement in abd circumference.
As I understand it from every bit of literature I've encountered on the subject, the trick is that it takes BOTH. You gotta eat in such a way that you don't stimulate your body to store belly fat specifically i.e. keep your blood sugar ultra stable, AND you have to exercise in such a way that you encourage your body to store the fat it does need in the places where it needs quick access to fuel the most i.e. in and around the large muscle groups. Since those muscles are active, they will require more and more glycogen for fuel. This means that in general you will store "excess" carbs as glycogen instead of fat as well so your overall body fat percentage will drop too.