After a good abdominal workout it's always a perfect idea to end with a core muscle stretch. No matter what type of exercise session you just finished, you can be sure that you somehow utilized this area of the body so cooling down will be important not only to prevent injuries but also to increase your range of motion.
A great core muscle stretch is done by first laying stomach down on a mat. Then place your hands directly under your shoulders with the elbows bent and slowly begin to press up so your upper body rises towards the ceiling. Note that your legs should stay straight the entire time and it is best if you also simultaneously think about squeezing your bum.
Take a few breaths in and out while you do this to help you feel the core muscle stretch even more. After holding for about ten to thirty seconds, lower the body again and repeat when ready.
Another exercise to perform is the side bend. Note that when you do these you do not want to lean back all that much as it can place additional strain on the back joints. To start, place your hands on your hips or alternatively straight out to the side. Your feet should be slightly wider than shoulder width apart to give you a good balanced stance. Next slowly begin to tilt your body over to one side until you feel a slight pull all along your side. After you've held this for a moment, switch back over and repeat on the other side.
Always ensure that you do not forget the lengthening training aspect of your workouts. Far too many people get all caught up in the contraction portion (the actual lifting) and forget that relaxation from this is also key to seeing results.