Perl for the Web
   Online book. The book provides tools and strategies to improve the performance of existing Web applications in Perl. Chapters 10 and 11 are relevant to mod_perl.
   http://www.globalspin.com/thebook/

Practical mod_perl
   Book by Stas Bekman and Eric Cholet; full text freely available in HTML and PDF under a creative-commons license.
   http://www.modperlbook.com/

The mod_perl Developer's Cookbook
   Companion site to the book, The mod_perl Developer's Cookbook. Information about the book, sample chapters and example code, and a list of resources.
   http://www.modperlcookbook.org/

Writing Apache Modules with Perl and C
   The home site of "Writing Apache Modules with Perl and C", a book about creating Web server modules using the Apache API, written by Lincoln Stein and Doug MacEachern.
   http://www.modperl.com