The "core" is the bodies foundation of strength. It is no wonder that all of the recent buzz in the fitness industry is on how to build a strong, athletic core. Not only will a flat, hard stomach look good, it will also prevent lower back issues and increase performance. Here is a sample of a core circuit that will help you in your quest for a more functional midsection.
V-Ups x 10
Sprinters x 10 (lying flat on your back, mimic a sprint movement. crunching upwards with the left leg and right arm. then crunching up the right leg and left arm)
Toe Touches x 10
Reverse Crunches x 10
Perform each movement one after the other with minimal rest. After completing the reverse crunch, rest 60 seconds before completing the circuit again. Perform the circuit 3-4 times total. Goodluck!