CPAN
CPAN is the magic bullet that all other languages envy.
It's a vast repository of modules that people have contributed.
It stands for Comprehensive Perl Archive Network.
Search for modules at search.cpan.org
http://search.cpan.org is the standard front-end to search the CPAN. It also includes links to most of the rest of these sites.
Find opinions about modules at cpanratings.perl.org
http://cpanratings.perl.org lets you rate and comment on modules and see what others thought of them, before you try.
Report bugs at rt.cpan.org
Submit your bug to RT at http://rt.cpan.org.
Annotate module documentation at annocpan.org
http://annocpan.org lets you annotate the documentation for a module, with the hope that the author will incorporate the changes in the future.
Find old versions of modules on the BackPAN
http://backpan.cpan.org/ has every module ever on CPAN, even if it's old and out of date.