Information Architecture for the World Wide Web

Louis Rosenfeld, Peter Morville. Now in its second edition, undoubtedly the best introduction to IA.
amazon.co.uk / amazon.com

Information Architects

Richard Saul Wurman.
amazon.co.uk / amazon.com

Practical Information Architecture

Eric L. Reiss.
amazon.co.uk / amazon.com

Information Architecture: Blueprints for the Web

Christina Wodtke.
amazon.co.uk / amazon.com

Mapping Web Sites

Paul Kahn, Krzysztof Lenk. A suprisingly badly designed book, but packed full of very inspirational information architecture examples, from isometric site-maps to flow charts and wireframes.
amazon.co.uk / amazon.com

Dynamics in Document Design

Karen A. Schriver.
amazon.co.uk / amazon.com

Content Critical

Gerry McGovern
amazon.co.uk / amazon.com

The Web Content Style Guide

Gerry McGovern
amazon.co.uk / amazon.com

Web Navigation

Jennifer Fleming.
amazon.co.uk / amazon.com

Sorting Things Out

Geoffrey C. Bowker, Susan Leigh Star.
amazon.co.uk / amazon.com

The Intellectual Foundation of Information Organization

Elaine Svenonius
amazon.co.uk / amazon.com

Laws of the Web

Bernardo A. Huberman.
amazon.co.uk / amazon.com

Infosense: Turning Information into Knowledge

Keith Devlin.
amazon.co.uk / amazon.com

The Social Life of Information

John Seely Brown, Paul Duguid.
amazon.co.uk / amazon.com