Sketching in ZBrush for Designers - Free Chapter
Jose Cuahas released a free chapter from his Sketching in ZBrush for Designers tutorial.
ZBrush SIGGRAPH 2013 Recap
Here is a massive recap of ZBrush's presentations from Siggraph 2013.
ZBrush Professional Tips and Techniques
Learn to work effectively and creatively with all versions of ZBrush in this new book from Pixologic.