I agree with Jwrecker, and I would add hollow body holds to that. Also, it's really essential to focus on contracting your abs, as you may find yourself initiating the movement with your hip flexors if you don't pay close attention.
On a broader note, abs are 90% diet and 10% ab training -- it doesn't really matter how much muscle you have if you can't see it. If you want to get abs, it's really key to eat less and do a high amount of high intensity exercise like resistance & power training to maintain a caloric deficit and therefore reduce your bodyfat %. Good luck!