Information Design

Envisioning Information
by Edward R. Tufte
Publisher: Graphics Press (May 1990)
ISBN: 0961392118
Covers the theory and practice of information graphics. Brilliant.

Don’t Make Me Think: A Common Sense Approach to Web Usability (2nd Edition)
by Steve Krug
Publisher: New Riders Press; 2 edition (August 18, 2005)
ISBN: 0321344758
During his five years in usability consulting and testing, Krug observed how people actually use the Web rather than how we *think* they use it. His book is based on empirical observation not exhaustive statistics.