Scissor Kicks.php

Scissor kicks are a great way to train your legs, hips and lower abs. Simply lie down and lift your head and shoulders off the ground. Now raise your feet and start opening and closing your legs (keeping your legs straight, but not locked) at a solid pace - making sure to cross your ankles on the closing motion.

You can place your hands underneath your gluteus maximus area (a.k.a. your butt) for balance and support, but you don't have to.

Cranking it up a notch
To increase the workload of the scissor kick, you can use ankle weights (don't overdo this, your knees won't like that) or you can move your legs up and down real slowly while maintaining the subtle kicking motion in your feet - basically combining it with a leg raise.

Other ab exercices
Flutter Kicks
Hanging Leg Raises
Leg Raises
Medicine Ball Sit Ups
Russian Twists
Sit Ups