Exercise of the Day: V leg raises.
One of the absolute greatest exercises I have ever done for lower abs would have to be the V leg raise. I came up with it myself and it will transform your lower abs. To do this exercise you begin to do a leg lift, but instead of coming straight up, you bring your legs up like a V. Splitting them apart as you move up will put an extra strain on your lower abs making them work twice as hard for the same exercise. It is a great way to work those lower abs.
Perform 3 sets of 10 reps for maximum results. Best of Luck!