The best abs workout is one which will give you the results you want. The most effective ones are the captain's chair, bicycle crunches, ball crunches, torso tack, reverse crunches, plank and the abs roller.
The best ab workout I have ever seen is in the P90X workout system. It is called Ab Ripper and is a very intense workout. You can find most of the ab exercises on the Ab Ripper workout online. I have also seen the results from the 8 minute abs workouts and seen great results with that as well. The site listed below will give you most of the exercises in both video's and workout routines. Just push yourself to do each exercise for each of your ab workout sessions. You can find more info at: www.fullfitness.net