If you want your site to reach its full potential it’s important that you have an understanding of how your visitors interact with it. Making your site easy to use can have a massive effect on conversions, sales or whatever goals you may have.
Here are a selection of excellent books covering the subject of usability and interaction design to get you started:
About Face 3: The Essentials of Interaction Design
by Alan Cooper, Robert Reimann David Cronin
Web Style Guide: Basic Design Principles for Creating Web Site
by PJ Lynch
Constructing Accessible Web Sites
by Jim Thatcher
Cost-Justifying Usability
by Randolph G. Bias and Deborah J. Mayhew
Defensive Design for the Web
by 37signals, Matthew Linderman, Jason Fried
Deliver First Class Web Sites: 101 Essential Checklists
by Shirley Kaiser
Designing Easy-to-use Web Sites: A Hands-on Approach to Structuring Successful Websites
by Vanessa Donnelly
Designing for Interaction: Creating Smart Applications and Clever Devices
by Dan Saffer
Designing Interactions
by B Moggridge
Designing Interfaces: Patterns for Effective Interaction Design
by Jenifer Tidwell
Designing the Obvious: A Common Sense Approach to Web Application Design
by Robert Hoekman
Designing the User Interface: Strategies for Effective Human-Computer Interaction
by Ben Shneiderman, Catherine Plaisant
Designing Visual Interfaces: Communication Oriented Techniques
by Kevin Mullet and Darrell Sano
Don’t Make Me Think: A Common Sense Approach to Web Usability
by Steve Krug
Emotional Design: Why We Love (or Hate) Everyday Things
by Donald A Norman
Envisioning Information
by Edward R. Tufte
Handbook of Usability Testing: Howto Plan, Design, and Conduct Effective Tests
by Jared Spool, Jeffrey Rubin, Dana Chisnell
Handheld Usability
by Scott Weiss
Human Factors in Product Design: Current Practice and Future Trends
by W. Green, Patrick W Jordan, Patrick W. Jordan
Information Visualization: Design for Interaction
by Prof Robert Spence
Human-Computer Interaction: Concepts And Design
by J. Preece, Y. Rogers, H. Sharp, D. Benyon, S. Holland, T. Carey
Prioritizing Web Usability
by Jakob Nielson and Hola Loranger
Readings in Human-Computer Interaction: Toward the Year 2000
by Saul Greenberg
Shaping Web Usability: Interaction Design in Context
by Albert N. Badre
Submit Now: Designing Persuasive Web Sites
by Andrew Chak
The Art of Innovation: Lessons in Creativity from IDEO, America’s Leading Design Firm
by Tom Kelley, Jonathan Littman, Tom Peters
The Design of Everyday Things
by Donald A. Norman
Human-Computer Interaction Fundamentals
by Andrew Sears, Julie A. Jacko
The Humane Interface: New Directions for Designing Interactive Systems
by Jef Raskin
The Inmates Are Running the Asylum:
Why High Tech Products Drive Us Crazy and How to Restore the Sanity
by Alan Cooper
Non-Designer’s Design Book
by Robin Williams
Homepage Usability: 50 Websites Deconstructed
by Jakob Nielsen and Marie Tahir
Thoughtful Interaction Design: A Design Perspective on Information Technology
by Jonas Löwgren and Erik Stolterman
The Design of Sites: Patterns for Creating Winning Web Sites
by Douglas K. van Duyne, James A. Landay, and Jason I. Hong
Usability Engineering (Interactive Technologies)
by Jakob Nielsen (Paperback – Sep 23, 1993)
The Usability Engineering Lifecycle: A Practitioner’s Handbook for User Interface Design
by Deborah J. Mayhew
Usability for the Web: Designing Web Sites that Work
by Tom Brinck, Darren Gergle, and Scott D. Wood
User Interface Design: A Software Engineering Perspective
by Soren Lauesen
User Interface Design for Mere Mortals
by Eric Butow
Web Application Design Handbook: Best Practices for Web-Based Software
by Susan Fowler and Victor Stanwick
Web Bloopers: 60 Common Web Design Mistakes, and How to Avoid Them
by Jeff Johnson
Web ReDesign 2.0: Workflow that Works
by Kelly Goto and Emily Cotler
Web Site Usability: A Designer’s Guide
by Jared M Spool, Tara Scanlon
My name is Christopher Lee and I'm co-founder of the questions & answers community 
{ 2 comments… read them below or add one }
excellent, thanks for the list, will keep going for a while!
Nice list!
For the record, I wasn’t the author on the Handbook of Usability Testing. Jeff Rubin and Dana Chisnell did all the heavy lifting. I just wrote the foreword.
Jared