# Line 20-24
my $year   = $cgi->param('year')   ? encode_entities($cgi->param('year
+'),   '<>"') : '';
my $media  = $cgi->param('media')  ? encode_entities($cgi->param('medi
+a'),  '<>"') : '';
my $genre  = $cgi->param('genre')  ? encode_entities($cgi->param('genr
+e'),  '<>"') : '';
my $source = $cgi->param('source') ? encode_entities($cgi->param('sour
+ce'), '<>"') : '';
my $title  = $cgi->param('title')  ? encode_entities($cgi->param('titl
+e'),  '<>"') : '';
[download]

# How I'da dunnit:
my %param = map {
    $cgi->param($_)
      ? ($_ => encode_entities($cgi->param($_), ''))
      : ()
    } qw(year media genre source title);
[download]

# Line 33-39:
if ( $year || $media || $genre || $source || $title ) {
  my @selections;
  push @selections, qq($title)  if $title;
  push @selections, qq($year)   if $year;
  push @selections, qq($media)  if $media;
  push @selections, qq($genre)  if $genre;
  push @selections, qq($source) if $source;
  ...
[download]

# How I'da dunnit:
if (keys %param) {
  my @selections = values %param;
  ...
[download]

As for verything from line 82 onward, i.e. the whole page(...) thing, I'd look into a templating system. Template Toolkit follows the Perl philosophy (easy things easy, hard things possible) pretty neatly in my opinion.