Crunches are great for ab toning, but if you are looking to flatten your tummy you should look for cardio workouts that have the extra benefit of working your midsection.

For example, both tae kwon do and kickboxing can provide a rigorous aerobic workout -- and the powerful kicks bring your abdominal muscles into play. Rebounding classes combine cardio with balancing exercises that strengthen the torso's core muscles. And even some lighter, recreational dance activities -- such as belly dancing (the name says it all) -- have the added plus of working your abs.