6) Cable crunches

An exercise which is still fairly common in most gyms. It works the whole length of the abdominals.
The subject grasps a cable attached to an overhead pulley. He/she holds its ends in front of his/her forehead then slowly leans forward by letting the abdominals do all the pulling and curling the back as if trying to curl up into a ball.
At the bottom of the motion he/she holds the contraction a bit, the slowly lets the cable back up.
Extra considerations: do not cheat by pulling the cable down using the triceps.