I have always heard and believed the old saying that "abs are made in the kitchen". However, I am one that struggles constantly with my diet, so...for working my abs I generally tend to rely on a few key exercises - bicycle crunches (I do 4 sets of 30), stability ball crunches (4x30), prone planks (3 @ 1 minute), side planks (4 @ 30 seconds), and this one ab machine at my gym that I like to do.