Is there some easy way to get cpan to tell me what modules are available?

Use cpanp -m regex

$ cpanp -m App::Ack
   1 App::Ack                       1.96     PETDANCE
   2 App::Ack::Plugin                        PETDANCE
   3 App::Ack::Plugin::Basic                 PETDANCE
   4 App::Ack::Repository                    PETDANCE
   5 App::Ack::Repository::Basic             PETDANCE
   6 App::Ack::Resource                      PETDANCE
   7 App::Ack::Resource::Basic               PETDANCE
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Or, start cpan, and type h, to get interactive help, but remember, cpan -m is not the same as cpan> m

cpan[1]> m /App::Ack/
  Database was generated on Thu, 24 May 2012 20:07:03 GMT
Module  = App::Ack               (PETDANCE/ack-1.96.tar.gz)
Module  = App::Ack::Plugin       (PETDANCE/ack-1.96.tar.gz)
Module  = App::Ack::Plugin::Basic (PETDANCE/ack-1.96.tar.gz)
Module  = App::Ack::Repository   (PETDANCE/ack-1.96.tar.gz)
Module  < App::Ack::Repository::Basic (PETDANCE/ack-1.96.tar.gz)
Module  = App::Ack::Resource     (PETDANCE/ack-1.96.tar.gz)
Module  < App::Ack::Resource::Basic (PETDANCE/ack-1.96.tar.gz)
7 items found
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A CPAN mirror has a file /modules/03modlist.data.gz which lists all the available modules.

Moritz, /modules/03modlist.data.gz is "The Registered Module List", an antiquated collection of officially approved modules. It was out of date back in 2004 when I first wrote suggesting to get rid of it.

The list that the OP wants is /modules/01modules.index.html.

xoxo,
Andy

#!/usr/bin/perl

BEGIN {
        $| = 1;
}

use strict;
use warnings;
use CPAN;
use Term::ANSIColor::Print;

my $print = Term::ANSIColor::Print->new();

my $d = shift @ARGV;
foreach $d (CPAN::Shell->expand("Module", "/./")) {
$print->bold_black( "\n\tmodule: ", $d->id), 
$print->dark_blue( "\tauthor: ", $d->cpan_userid),
$print->bold_black("\tcurrent version: ", $d->cpan_version),
$print->dark_green( "\tinstalled version: ", $d->inst_version), 
$print->dark_red( "\t", $d->inst_file); 
}
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