UPDATE: added check for ' ' to prevent warnings (thanks for testing, hacker)

use strict;
use warnings;

use POSIX;
use CGI qw(:standard);
use Calendar::Simple;
use DBIx::XHTML_Table;

my $today   = strftime("%d",localtime);
my $caption = strftime("%B %Y",localtime);

print header, start_html('simple calendar');
print DBIx::XHTML_Table
   ->new([calendar],[qw(Su Mo Tu We Th Fr Sa)])
   ->modify(table=>{border=>1})
   ->modify(caption=>$caption)
   ->map_cell(\&mark_today)
   ->output
;
print end_html;

sub mark_today {
   my $day = shift;
   return $day if $day eq ' ';
   return $day == $today ? u($day) : $day;
}
[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)