the key to abs, imo, is using weights.. your abs are muscles and you wouldn't do bicep curls without weight, would you?

i lay flat on my back on the bench, hang my legs off, put a 20 lb dumbell in between my feet and do leg lifts.. keep your legs straight.. i do about 3 sets of 15.

then i'll do decline sit ups with a plate on my chest.. you can do variations and turn at the top to get a bit of an oblique workout in too..

those are my main ab workouts and i add variations in here and there.. these are the workouts that gave me a six-pack and will stick by them..