Exercise Ball Roll
This one is relatively easy and fun. Lie with your stomach on an exercise ball and your toes on the ground. Move forward so that your chest is on the ball and stop when you get near your neck. Roll back so your stomach is at the midpoint of the ball. Repeat this five times.
Exercise Ball - Dumbbell Curl
Sit on an exercise ball and put your feet on the ground. Maintain your balance as you do curls with 5- or 10-lb. dumbbells. As you curl the weights in your right arm five times, tense your stomach area. Then do the same with your left arm. Do 10 curls altogether, five in each arm.
Sit-ups With Lower Legs on Bed
Sit-ups are great, but as you get older doing crunches are too taxing to do with any regularity. However, put your lower legs on a bed and your posterior on the corner of a couch, and lift up with your upper body about 6 inches. Do this 15 to 20 times and take a break. Repeat the set.