there was one I saw on the EAS site years back..I think it's called shutterbug or something like that. AMAZING burn, done on the floor. You look ridiculous doing it, but its killer. You basically start in crunch position, and simultaneously bring one bended knee towards your chest and the opposite arm towards your PLANTED knee, (keep the lifted appendages
parallel to eachother, this is NOT elbow to knee) then simultaneously lower both appendages back to start position. This excersise feels incredible, but you have to have no shame to do it in a packed gym
I prefer the crunch machine, weighted with plates at the ankle rest and above the shoulders.
machines aside nothing beats the stability ball for my upper abs. You get greater range of motion on a ball as opposed to the floor.
Doesnt really do jacks#it for my lower abs though.