Kevin Mullet and Darrell Sano, Designing Visual Interfaces
A good overview of the application visual principles to the design of user interfaces. This includes topics like hierarchy, balance, harmony, etc. An especially interesting section discusses various visual attributes (hue, value, size, orientation, shape, position, and texture) and their perceptual properties (e.g. we can instantly pick out objects of a particular color, but not shape, from a mixed collection). The diagrams feel old-fashioned, but give an appreciation for the clarity and consistency of the original Mac interface. The color plates are mostly wasted on examples of bad design or diagrams found elsewhere in the book. For better illustrations and an excellent discussion of these same principles applied to data presentation as opposed to UI design, see Edward Tufte's books, especially Envisioning Information.
For more information on Designing Visual Interfaces, see these excerpts and diagrams.