Crunches on "Flat" Setting
Crunches on "Rolled" Setting
Elbow To Knee Crunch
Do a minimum of three sets and make fatigue become your reps.
What does that mean? Simple, go until you can't go no more. Feel the burn, get tired, what ever! You should never limit yourself to just 10 reps when performing abdominal work because they are endurance muscles. So go the distance.