I'd tell you some super fancy way to gain a visible 6-pack, but I'll just tell you the way I got my midsection cut up. (For the ladies of course...
All I do is jump rope. I swear to you it's the MOST under-utilized way to achieve results in your abdomen region. Mind you, you can't just do something like 3 sets of 50 without stopping. My normal daily cardio regimen looks like this: wake up - run 2 miles (usually equates to 20-22 minutes)...eat breakfast, take my dog for a walk (25-40 min. at most), then I do 10 sets of 100 jumps without stopping. It equals out to 1,000 jumps perfectly. Has worked wonders for me, for I'd say at least the last year and 1/2.
Try it out (the jump rope part...but you can do the running and whatnot if you choose to).
Lemme know what happens. Best Of Luck bud.