XP and Agile Process References
Some references are linked to their respective Google Books preview.
Main Description

AUE01 Ken Auer et al. 2001. Extreme Programming Applied: Playing to Win. Addison-Wesley Publishing Co. 
Experiences from pioneers in applying XP.
BEC00 Kent Beck 2000. Extreme Programming Explained. Addison-Wesley Publishing Co.
Good introduction to the fundamental ideas of XP.
BEC01 Kent Beck, Martin Fowler 2001. Planning Extreme Programming Addison-Wesley Publishing Co.
Explains how to plan and manage an XP project.
COC01 Alistair Cockburn 2001. Agile Software Development Addison-Wesley Publishing Co.
Peers into the team dynamics, the cultures, the communications aspects of software development.
FOW99 Martin Fowler et al. 1999. Refactoring: Improving the Design of Existing Code Addison-Wesley Publishing Co.
JEF01 Ron Jeffries, Ann Anderson, and Chet Hendrickson 2001. Extreme Programming Installed. Addison-Wesley.
This book describes practical Extreme Programming techniques.
KER01 Norman L. Kerth, April 2001. Project Retrospectives: A Handbook for Team Reviews. Dorset House. 
"Presents a convincing argument for the value of taking the time to study past projects and learn from them [...] Kerth's sensitivity to the complex interpersonal issues surrounding project retrospectives will help any facilitator, participant, or manager get the most out of these important learning activities." Karl E. Wiegers, February 8, 2003.
KRO03 Per Kroll and Philippe Kruchten 2003. The Rational Unified Process Made Easy, A Practitioners Guide to the RUP. Addison Wesley Longman. 
A practical guide to adopting the spirit, principles and practices of the RUP. An invaluable resource in helping you decide how to apply the RUP in your organization or project.
NEW01 James Newkirk and Robert Martin 2001. Extreme Programming in Practice. Addison-Wesley Publishing Co. 
A report of experience using XP on a web project.
SUC01 Giancarlo Succi, Michele Marchesi 2001. Extreme Programming Examined. Addison-Wesley Publishing Co. 
A collection of papers covering a wide variety of topics related to XP.
WAK01 William Wake 2001. Extreme Programming Explored. Addison-Wesley Publishing Co. 
Based on the popular XPlorations website. Specific subjects are explored in detail.