Anyone who consistently works his/her abs muscles knows that you have to hit multiple muscle groups within that region and this cannot be achieved by doing just sit-ups. The sides of the abs (the obliques) are very crucial to getting that shape right and getting the strength you need in your ab region. Here are a couple of exercises to really help build those oblique muscles:
This exercise works the biceps and obliques and even gets a bit of leg in there:
This exercise focuses a lot on the obliques and the upper body as well:
Try both for 3 sets of 10 on each side.
Cheers Eights & Weights!