# untested
foreach my $dir (@subdirs) {
        # if you have .. you have also .
        next if ($dir eq ".");
        next if ($dir eq "..");

        my @files = File::Find::Rule->file()->name('*.*')->in($dir);
        
        # compose a filename:
        # you probably need a path not just a name; you have not cd to the inside directory
        # many module can hadle this for you, but you can deal with a relative path too
        my $outputname = "./$dir/List.txt";
        
        # open ALWAYS a lexical FH using the 3 args form.. 
        open my $lexical_filehandle, '>', $outputname or die "Cannot write to $outputname";
        
        # print each filename to the listfile
        print $lexical_filehandle "$_\n" for @files;
        close $lexical_filehandle;
}#next dir will be processed



##</code><code>##

  find . -type d -maxdepth 1 | perl -lne "system qq(ls $_ > ./$_/_list.txt)"