Remember, the key is spinal flexion; aka spine moving forward. A regular crunch does just fine, or better yet get a medicine ball and get something below your lower back to get the greater range of motion. At the bottom of the motion, you should feel your abs stretching really good. Range of motion for abs is a big deal, in my opinion, because there's very little to start with in the first place. Calves are similar in this way. Would you rather calf raise off the floor or off a platform-- nuff said. Reverse crunches work too but try to minimize hip flexion as much as possible.
and your welcome, CC