Ab Shredder

This quote is very true but a workout like this one helps a ton! If you are wanting the ultimate ab workout do the following 2 times a week in addition to your other full body/cardio workouts. It is also nice to add any of these exercises to your other routines. 

Get ready to make those abs burn! 

Hanging Knee/Leg Raises: 10-12 Reps, 3 Rounds 
If you have a pull-up bar this is a great lower abdominal and entire core workout. Hang from the pull-up bar and lift your knees at moderate pace towards your chest. If you are advanced, keep your legs straight and lift them up as far as you can go (should be about a 90 degree angle). Pause at the top then release slowly.
30 seconds to 1 minute
Repeat 3 rounds

Mason Twists: 30 Reps, 1-3 Rounds (if form is lacking then stop!) Use a kettle-bell, dumbbell or weighted ball here
To start, sit firmly on your rear, bend your knees and lift your feet a few inches off the floor. Lower your torso to a V position. It's important to keep your abs pulled in to maintain balance.
Twist your torso from side to side and tap the kettle-bell/dumbbell/ball to the floor on either side. Torso and legs are to stay in the V shape and don't slouch. Make sure you breathe!
 A rep consists of one twist to one side, for example, a twist to the left side.
(you can even use a can of soup or something weighted if you don't have ANY sort of weights)
30 seconds to 1 minute
Repeat 1-3 Rounds

Swiss Ball Jack-knives: 15/10/10 Reps, 2-3 Rounds
This one is tough and takes balance. You will need a stability ball.
Start in a push up position with the top of your feet (shoelaces) on the top of the stability ball, legs straight and extended. While keeping your upper body steady and contracting your abs, roll the ball towards your chest until your quads are perpendicular with your butt. Make sure your back stays flat and doesn't arch or round very much.
Roll the ball back out and repeat.
After doing the center reps follow them by pulling your quads diagonally towards the left elbow, then roll back out to starting position. Do the same thing but on the right side. Alternate sides and do 10 reps on each side.
30 seconds to 1 minute
Repeat for 2-3 rounds

Stability Ball Crunches: 15 reps. 3 rounds.
Position yourself so that your mid-back is on the stability ball. Keep your feet flat on the floor, hip distance or
slightly wider apart. Knees bent and core strong.
Contract abs, lift up into a crunch and exhale at the top.
Make sure to not pull on your neck or wobble around.
30 seconds to 1 minute
Repeat for 3 rounds