Don't you have time to go to the gym and train you abs? You can do a wide variety of exercises at home, too. You don't even need any equipment. Below is a great fast and effective abdominal workout to start with that contains the following exercises:
V Crunch - 30 secs / 15 sec rest
Leg Raises - 30 secs / 15 sec rest
Towel Sit Ups - 30 secs / 15 sec rest
Do 3-4 rounds and do this routine 3-4 times a week.