To get some deep abs focus on exercises that not only contract the abdominal but stretch the muscles apart. My favorite 3 are hanging leg raises, pulley crunches and sides twists.
hanging leg raises: Hang from your hands, this will give maximum stretch. Bring your legs up perpendicular to your body without bending your knees.
pulley crunches: Use a high pulley and a two handed rope. While on your knees pull the down with you as your bring your forehead toward the ground.
side twists: Using a smaller barbell, position it behind your neck and twists firmly from side to side. This will reduce your waist line quickly and is great for men and woman.
What exercises have gotten you the best results ?