These books are concerned with the visual style or appearance of the interfaces you design.
Designing Visual Interfaces: Communication Oriented Techniques
The examples in this book may be dated - it was written when Windows 95 was an exciting idea - but the principles are as solid as they were then. Kevin and Darrell take the principles of graphic design and teach you how to apply them to interface design.
A more modern book, and there's always a chance that the methods will be dated in five years. That said, Adam and Steve show us many methods for making user interfaces look better. A very practical book full of exciting techniques.
Ordering Disorder: Grid Principles for Web Design
Most websites are designed using a grid. It's the easiest way to make sure your design feels like it was laid out intentionally. Khoi Vinh is a highly respected designer, and I have no doubt that he does a good job of teaching the reader about how to use grids for website design.