Simulation for the Social Scientist by Nigel Gilbert and Klaus Troitzsch, published by Open University Press in 2005 (second edition). This is a key introductory text to ABM and other simulation methods. The companion website includes a sample chapter and code for many of the models in the book, although different code examples are written in different programming languages. Find this book at a UK university library.
Agent-based Models, also by Nigel Gilbert, from the Quantitative Applications in the Social Sciences series published by Sage in 2008. A nice, short (and cheap) introductory guide to the field. Find this book at a UK university library.
Individual-based Modeling and Ecology by Volker Grimm and Steven Railsback published by Princeton University Press in 2005. The publisher's website includes the first chapter as a free download. Railsback and Grimm also wrote Agent-based and Individual-based Modeling: A Practical Introduction, published in 2012, which introduces agent-based modelling and model design using NetLogo. The website for this book again includes the first chapter as a free download as well as supporting materials for teachers. Find this book at a UK university library.
Agent-based Models of Geographical Systems by Alison Heppenstall, Andrew Crooks, Linda See and Michael Batty (several of whom are or were at the UCL Bartlett Centre for Advanced Spatial Analysis) published by Springer in 2012. A comprehensive volume dedicated to ABM, as well as its integration with geographical information systems for realistic models. You can buy a hard copy or find this book at a UK university library, but the full text of this book is available as a free download from the UCL website.
Design of Agent-Based Models: Developing Computer Simulations for a Better Understanding of Social Processes by Tomas Salamon published in Bruckner in 2011, provides advice on how to design agent-based models. Very useful for newcomers to the field. Sadly as of June 2013 this book isn't available at any UK university library.