Apache will do the file listing for you if there is no DirectoryIndex in a publicly available directory.

If you want more control, I'd suggest glob. or File::Find to get the lists and File::Basename to guard against malicious input and dress up the text, as ++grep suggests. Here are some fragments to get you started:

# Specify what directory is meant by a tag.
# Bogus tags will fail.to see anything undesirable
my %dirs = (
    foo => '/foo',
    bar => '/foo/bar',
    baz => '/quux',
);
# restrict to html
my @fles = glob $ENV{DOCUMENT_ROOT}.$dirs{$query->param('dire')}.'/*.h
+tml';

# print GET urls for this script
print join " / ", map
          {$query->a( { href=>$query->url() . "?dire=$_"}, $_)} keys %
+dirs;

# print file list
use File::Basename;
print map {$query->a({ href => $base_uri
                              . substr( ($_, 
                                      length( $ENV{DOCUMENT_ROOT} ))
                     }, basename( $_, '.html')
                    )
           . $query->br() . "\n"
           } @fles;
[download]

Warning, this is off the top of my head. Mostly untested.

After Compline,
Zaxo