subversion

Practical Subversion, Second Edition (Expert's Voice in Open Source)
$34.99
This is a good book, although not fantastic.
The best chapter is 'Best Practices' at chapter 6.
The other chapters are well explained but trivial.

Subversion 1.6 Official Guide - Version Control with Subversion
$39.99
The book "Subversion 1.6 - Version Control with Subversion" is the official guide and reference manual for the popular open source revision control technology. The new edition covers Subversion 1.6 with a complete introduction and guided tour of its capabilities, along with best practice recommendations. Version Control with Subversion is useful for people from a wide variety of backgrounds, from those with no previous version control experience to experienced system administrators. Subversion is the perfect tool to track individual changes when several people collaborate on documentation or, particularly, software development projects. As a more powerful and flexible successor to the CVS revision control system, Subversion makes life so much simpler, allowing each team member to work separately and then merge source code changes into a single repository that keeps a record of each separate version.

Subversion Version Control: Using the Subversion Version Control System in Development Projects
$49.99
I found this book covered well the basics and introduced some good practices. However overall the book might have been better organized. For example you have to read the whole book to understand what best practices to adopt, before going back to the chapter on installation.
The real case examples also lacked analysis.
Finally, the book is getting a bit old since it covers SVN 1.1 and SVN is now at version 1.4, and there is no online follow up/errata page from PHPTR.

Maven: The Definitive Guide
$34.99
If not for the fair amount of errors in the source code, I would have given it 5 stars.

The concept and explanation from this book is concise and with clarity. Extremely easy to follow and be proficient in Maven.