Here is a list of free User Experience books for you to enjoy.

Free to read online books on Interaction Design

1. Search User Interfaces– by Marti A. Hearst
2. Web Style Guide– by Patrick J. Lynch and Sarah Horton
3. Designing Interfaces– by Jenifer Tidwell (Most of the book is available online, not all of it, as pointed out by Amanda)
4. Designing Mobile Interfaces– by Steven Hoober and Eric Berkman
5. Thoughts on Interaction Design- by John Kolko. Contributions by Ellen Beldner, Uday Gajendar, Chris Connors and Justin Petro (no longer free)

Free to read online books on Human-Computer Interaction (HCI)

1. The Psychology of Menu Selection: Designing Cognitive Control at the Human/Computer Interface– by Kent L. Norman
2. Mental Models in Human-Computer Interaction: Research Issues About What the User of Software Knows– by John M. Carroll and Judith Reitman Olson (editors)

Free to read books on Web Accessibility

1. Just Ask: Integrating Accessibility Throughout Design– by Shawn Henry
2. Building accessible websites– by Joe Clark

Free to read online books on Information Architecture

1. Introduction to Metadata – by Tony Gill, Anne J. Gilliland, Maureen Whalen, and Mary S. Woodley
2. Introduction to Controlled Vocabularies: Terminology for Art, Architecture, and Other Cultural Works– by Patricia Harpring
3. Categories for the Description of Works of Art– by Murtha Baca and Patricia Harpring

Free to read online books on Design for development

1. Wicked problems: Problems worth solving– by Jon Kolko