Here I am sitting on an exercise ball. And those are great, but use them for support and add a little difficulty.
What I usually do is grab a 20-22 lbs dumbbell and hold it behind my head, instead of just locking hands to support my neck. Sit on the ball so that your butt is actually barely on it, with mostly your back and core supporting your balance. These crunches involve short movement forward, until yo feel a burning sensation in your upper abs and obliques. I usually do about 100 of those and feel the burn. The more, the merrier. You will get your abs to pop quite fast with these.