Bias, Randolph G. & D. J. Mayhew (eds.)
"Cost-justifying Usability"
(Academic Press 1994)
→ Good to learn from on how usability relates to costs and gains of a project.

Cooper, Alan:
"The Inmates are running the Asylum"
(SAMS 1999)
→ Learn more about persona - a great analytical tool that fits well with the needs that developers have of understanding their users from early on in the development process.

Kaasgaard, Klaus:
"Software Design & Usability: Talks with Bonnie Nardi, Jakob Nielsen, David Smith, Austin Henderson & Jed Harris, Terry Winograd and Stephanie Rosenbaum"
(Copenhagen Business School Press 2001)
→ Klaus has talked with some very interesting people and made it into a very interesting book - a great introduction to the many ways of thinking about design and usability.

Krug, Steve:
"Don't Make Me Think: Common Sense Approach to Web Usability"
(Roger Black 2000)
→ Funny and insightful. Includes "Usability testing the movie" ... Don't think about it - read it.

Nielsen, Jakob:
"Designing Web Usability"
(New Riders 2000)
→ Design simplicity and web usability that everybody in this field should know about.

Norman, Donald:
"The Design of Everyday Things"
(Doubleday Books 1990)
→ A classic that I warmly recommend to anyone who is interested in the relationship between humans and their things.

Nielsen, Lene: "From User to Character" (PDF, 7 pages, 320 Kb) (DIS2002, London, 2002)
→ Taking the very meaningful step from describing the user to constructing "live" characters.