Pod::Usage is great in conjunction with Getopt::Long. I'm not sure Getopt::Declare does both jobs.

Most of the POD-related modules are great, in fact — assuming you are properly diligent to create POD for the code you write.

CGI::Application makes CGI scripts that much clearer.

So does the Template Toolkit.

Class::DBI makes database use trivial.

The last three modules and misc utility modules available for them have enabled me to write a web database application with almost no code at all (inspired by Kake Pugh).

CGI::Untaint and Data::FormValidator make the tedious job of validating input much easier.

Imager is great for any kind of 2D graphics, particularly graphs (it will scale them and add grid and axes automatically). I've found it much nicer than GD and friends.