3D User Interfaces: Theory and Practice, Second Edition is now available. Written with my colleagues, Ernst Kruijff (Bonn-Rhein-Sieg University of Applied Sciences), Ryan McMahan (University of Texas at Dallas), Doug Bowman (Virginia Tech), and Ivan Poupyrev (Google ATAP), it is the updated edition to the only comprehensive text/reference book on 3D user interfaces.
Order your copy from Amazon, Barnes and Noble, or directly from Pearson.