Here are two really effective abdominal exercises for spot toning. You can’t spot reduce (lose fat in just one area) but you can definitely spot tone.
1. My favorite oblique (love-handle) movement. Not only does it give me a stretch it also helps keep my obliques defined. Tennis players love this one because this helps you stretch and strengthen the muscles you need for an explosive serve.
Take a weighted bar, not dumbbells, a bar over your head and stretch your hands up. Slowly lean to one side keeping your body as straight as possible. Lean as far as you can with control and slowly come back up.
2. Swiss ball abs crunches are intense and target the front six pack. You can do these any way you please. The important thing is to remember to life your chin to the ceiling not your neck. Doing about 100-200 reps define my abs without a doubt.