Don’t Make Me Think
Steve Krug
Good Books on UI
Roughly in order of their usefulness.
Smashing UX Design
Allen & Chudley
Designing Interfaces
Jenifer Tidwell
Designing Web Usability
Jakob Nielsen
Information Architecture for the World Wide Web
Peter Morville & Louis Rosenfeld
Web Navigation: Designing the User Experience
Jennifer Fleming
Web Usability and Navigation
Merlyn Holmes
Web Bloopers: 60 Common Web Design Mistakes and How to Avoid Them
Jeff Johnson
GUI Bloopers
Jeff Johnson
Accessible Web Sites
Thatcher, et al.