The Kick-out is one of the favorite core exercises because it pushes me hard. I struggle a lot with it, but I see the improvements in my core strength as well. See the video below for details. Note that you can do it with your palms on the floor on either side of your bum, or you can lift your palms off the floor if you are strong enough.
Sit on the floor, lift your legs in the air, and put your palms beside you. Pull your knees close to your chest and pull your chest towards your knees using your core strength. The release your knees forward without your feet touching the floor. Repeat.
Cheers Eights & Weights!