These are the animation rigs used in the first 2 chapters of the BlenderCookie training series "Animation Fundamentals in Blender"
http://cgcookie.com/training-series/animation-fundamentals-v1/ by Beorn Leonard.
This Blend file contains four complete rigs:
Ball with squash and stretch controls
Ball and chain
Ball with a tail
Each rig is ready to animate with all necessary controls