There are a number of modules on CPAN that have been designed to work as a plugin for CGI::Application. They usually export useful methods that you can use in your application module.
Some other modules are designed for use with CGI::Application, even if they do not call themselves a plugin:
The CGI::Application documentation has the primary reference for how to write a plugin. Here are some supplemental references.
Originally transferred from http://cgi-app.org/index.cgi?Plugins