Perl and mod_perl are constantly changing. To keep up to date with all the latest developments you can turn to a number of great web sites and mailing lists devoted to mod_perl.
The Apache Foundation's Apache/Perl Integration Project Site
All mod_perl developers have this site at the top of their bookmarks. Not only can you download the latest releases of mod_perl, you will also find a plethora of links and documentation.
The modperl Mailing Lists
The main mod_perl list, firstname.lastname@example.org, is a place where you can ask questions particular to any aspect of mod_perl - as with any mailing list of this sort, concise questions, with basic information on operating system, module versions, etc., will make answering such questions easier. The read-only list email@example.com sends out periodic announcements of interest to the mod_perl world. firstname.lastname@example.org is a list specific to promoting the use of mod_perl in general. The last two lists relate to mod_perl development - email@example.com is where to discuss more technical issues of mod_perl, including bugs and features, while firstname.lastname@example.org sends out a message when changes to the mod_perl cvs sources occur.
The Official Apache Module List
This is the official list of modules contributed to CPAN that are specific to mod_perl.
The mod_perl Guide
The mod_perl Guide, the latest version of which is available at this site, contains valuable information on how to set up and use mod_perl, and also describes some common pitfalls often encountered in a mod_perl environment.
These two quick reference cards contain information valuable to the mod_perl developer, such as mod_perl API methods, Apache configuration directives, and HTTP status codes.
ActiveState maintains ActivePerl, which has become the standard Perl binary release for Win32 (Linux and Solaris binary versions are also maintained). At this site you can find links to where to download these packages, as well as fairly complete set of documentation for Perl, including a FAQ for Win32 users.
The Comprehensive Perl Archive Network (CPAN)
CPAN (the Comprehensive Perl Archive Network) is the main repository for both the official Perl sources and also contributed modules. The first link above describes CPAN - see also the link to the CPAN Frequently Asked Questions (FAQ), which answers commonly asked questions about CPAN - while the other links are to CPAN search engines, including the documentation to most contributed modules.
This site maintains a copy of the standard Perl documentation, as well as that for most modules contributed to CPAN.
Perl Source Code
This is an experimental site that presents the perl source code in as a searchable, cross-referenced form.
General Perl Resources
These sites are the standard ones for Perl in general - here you will find news, articles, documentation, discussions, and links to other Perl sites.
These newsgroups contain discussions (often entertaining) about issues regarding Perl. comp.lang.perl.misc is for Perl in general, while comp.lang.perl.modules is for questions specific to Perl modules, including mod_perl. These two groups are unmoderated - comp.lang.perl.moderated is moderated, meaning that discussions generally are relevant to Perl and stay on topic.
General Apache Resources
These sites provide a wide variety of information on the Apache web server. You'll find downloads, documentation, discussion and other information.