The most important ingredients are diet and cardio. You probably already have a six pack, you just need it to 'pop'. Run, swim, play hoops, ride a bike, anything that gets your heart rate up for at least 20 minutes. Ab exercises are great for building a tighter more defined mid-section, but they wont make them any more visible than they are now. You gotta shed the fat bro.
So my answer would be cardio, diet, cardio, diet, cardio, diet.