MODO Squash and Stretch Ball Rig
Most artists interested in animation want to dive head first into character animation, but ask any seasoned animator and they’ll recommend the best place to start is animating a simple bouncing ball. Animating a ball allows you to focus on the core principals of animation and build a strong foundation for every animation you will create in the future.
Although you could use a simple sphere primitive to animate with, having a sphere rigged with built in squash and stretch capabilities will make it much more enjoyable and produce better results using fewer keyframes.
Below is a link to a rigged ball in MODO ready to animate.