UX Bookmark lists a few printed UX books that are available to read for free online, including the following.
- Search User Interfaces- by Marti A. Hearst
- Designing Interfaces- by Jenifer Tidwell
- Thoughts on Interaction- by John Kolko. Contributions by Ellen Beldner, Uday Gajendar, Chris Connors and Justin Petro
- The Psychology of Menu Selection: Designing Cognitive Control at the Human/Computer Interface- by Kent L. Norman
- Just Ask: Integrating Accessibility Throughout Design- by Shawn Henry
- Building accessible websites- by Joe Clark