Best Ab Strengthening Exercise?

Here is my FAVORITE workout to strengthen up my stomach muscles.
It's called a "Reverse Crunch."

All you need to do is lie on your back with your hands holding a bed, or a sofa, or something heavy enough to steady your upper body.

Extend your legs out straight, and lift your legs off of the ground about 5 - 9 inches.

Bring your knees toward your chest (as if you were balling up into a ball - bending your legs) and roll up onto your upper back, between your shoulders. Hold for a few seconds, and slowly return to the beginning position (with your legs slightly off the ground).

Do a few reps of this bad boy, and you'll really feel your abs working. Remember to keep your tummy tucked in, as if someone is poking you in the gut, and you're trying to keep your stomach away from their fingers.