Set up a defined dribbling area with cones or discs. I recommend 20-40 yards square depending upon age. Each player has their own ball. The game begins with all players dribbling around within the defined area. The coach then yells out a part of the body, such as "Elbow", and all players must stop dribbling and gain control of the ball with that body part. It sounds kind of silly, but especially younger kids think it's a ton of fun.

Don't hold back with the parts you call. The crazier the better. The ones I usually use include: Foot, Knee, Elbow, Forehead, Ear, Bottom, Stomach, Back of the Head ("Don't Fall Asleep!"), etc. You can also specify Right or Left (foot, knee, etc.) for an extra challenge.