My two cents..

Personally I would have to say that the most effective way of
flattening your stomach is a combination of strength training,
cardiovascular exercises coupled with a stable blood sugar and diet.
Sure lots of crunches and other ab exercises may give you great tone
and definition, but to see the best results you need to reduce the
layer of body fat covering up those visible cuts referred to as 'six-
pack' abs. I have a blog about getting flat abs and low calorie diets
if ya wanna check it out, its at http://flatabsfast.blogspot.com/