Honestly, as hard as it is to believe, ab exercises don't do as much for your abs as you would think. There are many supporting muscles that must be worked to stretch your skin in a way that causes your abs to show up more. The thing to remember is that your ab muscles are there no matter what; it's a combination of ab and other exercises that will make them show up more.
One thing that I would recommend which has helped me is the full, weighted squat. You'll need access to a rack with a barbell and a lot of weights, and will need to make sure that when you go down your legs bend parallel to the floor.
The full squat works out almost every major muscle group, and will work a lot of those muscles in your back and sides, as well as your core, and will work to make your abs protrude in the way you want them to.
I'd recommend looking into Mark Rippetoe's workout program; you can find his routine various places for free online and it is what I use.