Acme::              Joke and humor. Not for production code. 

Algorithm::         Algorithms, somewhat mathematical, that
                      don't fit into other cats. 

Alien::             Perl modules that install non-Perl code. 

Apache::            Apache web server. 

Astro::             Astronomy, star charts. 

...

Bundle::            Modules to install sets of other modules. 

Business::          Handling money or time, mostly within 
                      the Western, white-collar office life. 

Carp::              Report errors from caller's location. 

Catalyst::          Catalyst web application framework. 

CGI::               Common Gateway Interface.

CLI::               * see Getopt::

Config::            Configuration files. 

Crypt::             Cryptography. 

Data::              * 

...

Getopt::            Command line processing. 

GPS::               Global Positioning System.

HTML::              HyperText Markup Language generation. 

Image::             Images, graphic files (GIF, JPEG, PNG, etc.) 
                      Also PerlMagick/ImageMagick. 

IO::                Input/Output (but see also File::). 

...