What type of exercise to make your stomach flat?

Crunches work better than situps, although I have heard that they don't even work at all when flattening your stomach!

My doctor recommended this to me, you should try it. It's very simple. Incorporate it into your daily routine, you don't need to necessarily have to stop everyday and "exercise." Stand with your legs a few inches apart (not together--but enough to produce balance). Put both of your hands up, palms facing outward as if you're standing with your face against the wall and you're using your palms to touch the wall. Tighten your abs and turn your upper body left, then turn right, counting each of those as ONE. Move your upper body only! Be sure to move your head AND both arms along with each turn. The only part that should stay immobilized is everything from your waist and down! On day one, do one twist (left and right). Day two, do two. Add one more set each day. Do this before you shower, after you shower, after you used the bathroom, whenever. Be sure to keep your abs tightened while doing this exercise. Your abs will start to burn a little as if you had done crunches or sit ups laying down.