Envisioning Information by Edward R. Tufte
I got a copy of this book over the Christmas period (I now have all four of Tufte's books). This follows the pattern of the other three - beautiful production values, and an authoritative view (some might say didactic!) of design as applied to the graphical display of information. The book was originally published in 1990; the copy I have is the 10th printing from 2005.
The book has six chapters: Escaping Flatland, Micro/Macro Readings, Layering and Separation, Small Multiples, Color and Information, Narratives of Space and Time, and finally a brief Epilogue.