Hanging Knee raises, Leg lifts, ect, but these will just help develop your lower abs, not necessarily bring them out, that is mostly a function of BF%.
This reminds me, tonite I had the worst experience with my lower abs. I am on a Test/EQ/Dbol cycle, which sometimes leaves me so pumped in the gym I can barely move the bodypart I am working. Anyways, I decided to really crank out some Knee raises, and after I finished, I thought my appendix exploded----lower abs felt like they were cramping severely and I thought I was going to collapse. About a minute later it subsided, but I could tell they were still pumped. Terrible feeling with chicks on either side of me, I never felt anything like it before.