Here is a list of popular abdominal exercises for people trying to expand their ab workout.
How should you structure your abs workout
You should do abdominal exercises 2-3 times a week for 2-3 set of 10-15 repetitions. Choose 3 exercises that work all areas of your abs for a complete workout. You can vary the exercises you do to prevent your body from getting used to one movement.
Abdominal training exercises for the Upper Abs :
Exercise Ball Crunches - Sit on the exercise ball with your feet flat on the floor. Let the ball roll back slowly and lie back until your thighs and torso are parallel with the floor. Contract your abdominals raising your torso to no more than 45 degrees. Return to horizontal position. Repeat.
Cable Crunches - This exercise requires a triceps pushdown machine with a rope attachment. Kneel down in font of the machine holding the rope just above your head. Slowly crunch down to your right knee and hold for 2 seconds as you breathe out. Return to the start position slowly and repeat to the left knee.
Weighted Curls - Lie on your back with your knees bent and feet flat on the floor. Hold a medicine ball or weight plate to your chest. Curl up just enough to lift both your shoulders off the floor a few inches. Hold for a few seconds and return to the start position.
Abdominal training exercises for the Lower Abs :
Lying Leg Raises - If you have back problems consider reverse crunches instead of this exercise. Lie on your back with your hands, palms down under your buttocks. Raise your legs about 30cm (12") off the floor and hold them there. Now trying to use just your lower abs, raise your legs by another 15cm (6"). Make sure your knees are slightly bent, and that you are using your abs not your hips.
Hanging Knee Raises - You need a chin-up bar or something you can hang from for this. Grab the bar with both hands with a grip a bit wider than your shoulders, cross your ankles and bring your knees up to your chest. Pause at the top of the movement for a second and then slowly lower your knees by relaxing your abs. Don't lower your legs all the way. Repeat the movement using just your abs to raise your knees. - Make sure that you don't start swinging. You want your abs to do the work, not momentum. Make sure lower back stays neutral or slightly rounded, not arched, and that your abs are doing the work, not your hips.
Captain's Chair - This exercise requires gym equipment. Start with legs dangling and slowly lift your knees in toward your chest. The motion should be controlled and deliberate as you bring your knees up and return them back to the starting position.
Abdominal training exercises for the Obliques :
The obliques, commonly known as the 'love handles' are an area that is often neglected. There are four popular ab exercises that work the obliques.
Lying Oblique Leg Raises - Lie on your right side on the floor on a mat and keep your left leg over your right, placing your right hand in a comfortable spot and your left hand behind your head. Bring your torso and left leg toward each other as you pull with your obliques. Squeeze for a one-count and return to the starting position.
Standing Side Bends - Begin by standing up straight with your feet shoulder width apart. You can hold a dumbbell in your left hand with your palms in. Keeping your back straight, bend to the left as far as you can, then return to the start position. Repeat for the opposite side. Remember to bend only at your waist.
Seated Barbell Twists - Sit at the end of a flat bench or in a chair with your feet firmly on the floor. Place a barbell (or a broom handle) on your shoulders, keeping your back straight and upright. Slowly twist your torso to the left, then to the right. Keep your back straight and your head up, keeping your abs constantly contracted throughout the entire exercise.
Cross-Knee Crunches - Like ab crunches, take the lying, bent-knee position, but this time crunch diagonally as if you are trying to touch each shoulder to the opposite hip alternately. At the top position, one shoulder and one hip should be off the ground. - This is a good exercise that works your obliques as well as your upper abs.