Chris Jone's 'Human Progress' project is one of the most popular topics on the Blender Artists forum with over 726k views. He regularly updates it, and recently posted an absolutely stunning video of an animated hand complete with wrinkles, veins and tendons.
He uses a tension map to model blood flow to allow for discoloration of the knuckles when the hang tightens into a fist. Read the new post on Blender Artists for in-depth information on how he achieved this.