"Rendering with mental ray & 3ds Max" is another excellent title from Focal Press, and a thorough overview of the mental ray rendering engine.
If you've ever tried to find comprehensive documentation of mental ray's features online, you've surely been disappointed. While blog posts and tutorials abound, it's difficult to find anything reference-grade. This book covers most of mental ray's features in quite a bit of detail, and does a good job explaining the input parameters and how they'll affect your scene.
Along the way you'll learn just enough theoretical detail about the major concepts - photons, ambient occlusion, global illumination, caustics,etc. - to put these controls in perspective.
This book isn't without its faults. The numerous rendered images and screenshots are helpful for illustrating how to achieve certain effects, but not all of them are great quality final renders. In a few cases, you'll wonder if the output they demonstrate is worth all the effort.
Also, although it's heavily skewed towards 3ds Max. If you're a Maya user, you'll recognize all of the renderer inputs and concepts, but the interface will be foreign and the book won't have much tutorial value.
Still, it's a great reference book if you're looking for a bit more detail on mental ray, or are frustrated trying to get quality renders out of it, regardless of your platform. And if you're a 3ds user, you should definitely have this one on your bookshelf.