Edward Tufte sees things most of us do not initially, then manages to render his vision in exquisitely illustrated, well-written texts. He identifies the attributes of effective communication of information and then illustrates what works and why in very understandable terms.
For instance, in his chapter "Layering and Separation," Tufte dissects the problems with array of marshaling signals then reworks the presentation and provides a step-by-step explanation of his process. His coining of the wonderful notion of an "information prison" shows that his cleverness extends from the visual to the written.
As Tufte writes in his introduction, "The principles of information design are universal-like mathematics-and are not tied to unique features of a particular language or culture." He proves this point amply by drawing on myriad sources and examples.
His comments and insights of the power of color are especially enlightening, and if you have ever been subjected to a particularly hideous PowerPoint slide show where the presenter got more than a bit carried away with the technology, you will be agreeing more than disagreeing with the ideas here.
Finally, I acknowledge there is bound to be some sticker shock associated with Edward Tufte's books. But if you consider the amount and quality of color (which requires special press runs), the quality of the paper, the amount of press time (Tufte oversees and approves the printing), and the vast scope of timeless information contained in each book, then these books are a deal.