10 Most Effective Ab Excercise: #8 Full Vertical Crunch

In a full verticul crunch, you really work the abs by involving both the upper and lower body. To do it right:

1. Lie on your back and extend the legs up towards the ceiling.
2. Place hands behind your head (lightly cupping it) and contract the abs to lift the shoulder blades off the floor.
3. At the same time, press the heels towards the ceiling, creating a 'u' shape with the torso.
4. Lower down and repeat for 12-16 reps.

(extracted from exercise.about.com)

10 Most Effective Ab Excercise: #7 Reverse Crunch

It may seem like the reverse crunch is for the lower abs but, remember, the rectus abdominis is one long muscle, so you can't separate upper from lower. To do this move right:

1. Lie on the floor and place hands on the floor or behind the head.
2. Bring the knees in towards the chest until they're bent to 90 degrees, with feet together or crossed.
3. Contract the abs to curl the hips off the floor, reaching the legs up towards the ceiling.
4. Lower and repeat for 12-16 reps.
5. It's a very small movement, so try to use your abs to lift your hips rather than swinging your legs and creating momentum.

(extracted from exercise.about.com)

10 Most Effective Ab Excercise: #6 Long Arm Crunch

This move, ranked 6th in the ACE study, emphasizes the upper part of the abs. To do it right:

1. Lie on a mat and extend the arms straight out behind the head with hands clasped, keeping the arms next to the ears.
2. Contract the abs and lift the shoulder blades off the floor.
3. Keep the arms straight and avoid straining the neck. If you feel neck pain, take one hand behind the head while keeping the other arm extended.
4. Lower and repeat for 12-16 reps.

(extracted from exercise.about.com)

10 Most Effective Ab Excercise: #5 Torso Track

The Torso Track is a tough exercise because it can hurt your back if you're not careful.

1. Grip the handles of the Torso Track and pull the abs in without holding your breath (as though bracing them).
2. Exhale and glide forward as far as you comfortably can. If you collapse in the middle and feel it in your back, you've gone too far.
3. Contract the abs to pull your body back.
4. Add tension by using more tension chords.

(extracted from exercise.about.com)

10 Most Effective Ab Excercise: #4 Vertical Leg Crunch

The vertical leg crunch is another effective move for the rectus abdominis and the obliques. To do it right:

1. Lie face up on the floor and extend the legs straight up with knees crossed.
2. Contract the abs to lift the shoulder blades off the floor, as though reaching your chest towards your feet.
3. Keep the legs in a fixed position and imagine bringing your belly button towards your spine at the top of the movement.
4. Lower and repeat for 12-16 reps.

(extracted from exercise.about.com)

10 Most Effective Ab Excercise: #3 Exercise Ball Crunch

The exercise ball is an excellent tool to strengthen the abs and comes out number three for working the rectus abdominis. To do it right:

1. Lie face-up with the ball resting under your mid/lower back.
2. Cross your arms over the chest or place them behind your head.
3. Contract your abs to lift your torso off the ball, pulling the bottom of your ribcage down toward your hips.
4. As you curl up, keep the ball stable (i.e., you shouldn't roll).
5. Lower back down, getting a stretch in the abs, and repeat for 12-16 reps.

(extracted from exercise.about.com)