Assume a basic push-up position, but rather than keeping both hands on the floor place the medicine ball underneath one of your palms. Do a push up, then roll the ball over to the opposite hand, and repeat the motion. This exercise is good because it incorporates more muscle groups than a standard push-up. In addition to working the chest, triceps and shoulders you will feel your core being activated as well.
Medicine Ball Cross-Over Push-Up - Start Position
Medicine Ball Cross-Over Push-Up - Finish Position