Whats the best exercise for the lower abs?

Deadlifts.

What makes you think there's a strength deficiency? If you want to reveal abs, lose fat.

Lifting your legs in various ways will get the lower abs pretty good.

Planks and leg raises are all I do for abs. My abs are involved in about every exercise I do, so I don't do a lot of separate ab work.

There is no such thing as lower and upper abs in regards to exercise. There are abs. Don't believe me, look at their insertion points.

bump

From pilates; I knew I couldn't describe it, so here's a video.

http://video.about.com/exercise/Best-Lower-Ab-Exercises.htm

The double dip is a killer.....

Thank you for the recommendation as this is perfect for knee injuries!! Love pilates and can't wait to get back in my exercise routine when I recover from my knee injury