The bicycle crunch is one of the most effective exercises to sculpt your abs. It works all the abdominal muscles.
Start by lying on your back with your hands behind your head and bring your legs up to a 90 degree angle. Pull your left knee into your chest and bring your right elbow to your knee. As you are pulling the left knee to the right elbow you should extend your right leg. Keep alternating in a controlled movement. Do the first 10 reps slow stopping after every two. So you go left knee to right elbow, right knee to left elbow, then you stop and you repeat. After 10 reps do the remaing without stopping but still in a slow controlled movement. To avoid hurting or straining your neck be careful not to pull your neck forward. Do 3-4 sets, 20 reps.