This is one I tried for the first time a few days ago. Dr. Ryan Smith has been making the trip out to bench with us, so I've been using his expertise to come up with new movements that will help build and stabilize my pecs and shoulders. I come up with the stuff and then ask his advice. Right away I knew this movement was a winner.
Since I've torn or injured my pecs more times than I've seen Paris Hilton on TV, I've been looking for a movement that would completely isolate the pec region without having to rely on a one dimensional pec-deck machine.
To do this movement you'll need to get some type of ankle cuff.
I personally like the leather version but have had a hard time finding them, so nylon may be the best bet. I also found the incline bench to offer a better range of motion with the cable than a flat bench.
Attach a strap to each wrist and get on the bench. Keep your chest up high in the air like you have a string on your sternum pulling you toward the ceiling. Now do your flyes. Since you're not holding a dumbbell or cable handle, you can't lead with your hands or use your forearms to aid in the movement. You feel the pecs working right from the start and continue throughout the entire range.