Perl Debugged, by Peter Scott and Ed Wright (Addison Wesley). A good book on how to debug Perl code and how to code in Perl so you won't need to debug.
Debugging Perl: Troubleshooting for Programmers, by Martin Brown (McGraw Hill). This book tells you pretty much everything you might want to know about Perl debugging.
Programming Perl, Third Edition, by Larry Wall, Tom Christiansen, and Jon Orwant (O'Reilly). Covers Perl Versions 5.005 and 5.6.0. Chapter 20 talks in depth about the Perl debugger.
"Cultured Perl: Debugging Perl with ease, catch the bugs before they bite," by Teodor Zlatanov: http://www-106.ibm.com/developerworks/library/l-pl-deb.html
This article talks about using the Perl command-line debugger, the GUI Devel::ptkdb, and a special Perl shell for debugging.
The Mythical Man-Month, 20th Anniversary Edition, by Fred P. Brooks (Addison Wesley). A must-read for all programmers. After reading this book, you will at least learn to plan more time for the debug phase of your project.
General software-testing techniques FAQ: http://www.faqs.org/faqs/software-eng/testing-faq/.