The bridge opposite arm-leg reach and the side plank are two good exercises for reducing abdominal fat, as reported by Health.com and Shape.com. These exercises can be performed without any additional equipment besides an exercise mat.
For the bridge opposite arm-leg reach, lie on your back with your left foot flat on the floor, your left knee bent, and your right leg stretched toward the ceiling. Extend your left arm toward the ceiling while keeping your right arm down by your side. Swing your raised leg to the right and raised arm to the left, and then return them to the center. After 10 to 12 reps, switch sides and repeat.
For the side plank, lie on your left side with your elbow directly beneath your shoulder and with your legs stacked. Place your right hand on your left shoulder or on your right hip. Raise your hips until you are balancing on your forearm and feet with your body forming a diagonal line. Hold this position for as long as you can and then repeat until you have held for 30 seconds total. Switch sides and repeat.