Target Mission: The Lower Abs

As I've been reading and researching, it would seem that some muscles are more difficult to target than others. Apparently this is especially true for the lower abdominals. Crunches don't do it, sit-ups, don't do it, so what can be done in regard to lower ab exercises to target these elusive muscles?

I found one of the best exercises (mainly because you can do it anywhere and don't need any gym equipment) is the simple leg raise. Lay on the ground with your body straight, bring the legs up, lower them back down without letting them hit the ground, easy as that.

Here's a video demonstration:



There are other exercises I would like to try but am not yet strong enough to do them. I am going to stick with these for the time being while focusing on my cardio and nutrition a bit more.