I took a look on the CPAN at Games::Dice::Die, and then at Games::Dice. It seemed like Games::Dice had many more features. So, I took a look at the code, and realized it was easy to add the support that you wanted. I only needed to slightly change the regex and 2 lines of code!
 Games/Dice.pm.old 20041217 14:17:54.172707400 0500
+++ Games/Dice.pm.new 20041217 15:56:22.599186000 0500
@@ 19,7 +19,7 @@
sub roll ($) {
 my($line, $dice_string, $sign, $offset, $sum, @throws, @result);
+ my($line, $dice_string, @throws);
$line = shift;
@@ 34,38 +34,29 @@
% # a percent sign for d% = d100
)
)
 (?: # groupingonly parens
 ([+xX*/bB]) # a +  * / b(est) in $2
 (\d+) # an offset in $3
 )? # both of those last are optional
+ ((?: # capture
+ [+xX*/bB] # a modifier
+ \d+ # a, number
+ )*) # capture
}x; # whitespace allowed
 $dice_string = $1;
 $sign = $2  '';
 $offset = $3  0;
+ @throws = roll_array( $1 );
+ return unless @throws;
 $sign = lc $sign;

 @throws = roll_array( $dice_string );
 return undef unless @throws;

 if( $sign eq 'b' ) {
+ my $mod = $2;
+ if( my($offset) = ($mod =~ /[bB](\d+)/) ) {
$offset = 0 if $offset < 0;
$offset = @throws if $offset > @throws;
@throws = sort { $b <=> $a } @throws; # sort numerically, d
+escending
 @result = @throws[ 0 .. $offset1 ]; # pick off the $offse
+t first ones
 } else {
 @result = @throws;
+ @throws = @throws[ 0 .. $offset1 ]; # pick off the $offse
+t first ones
+ $mod = '';
}
 $sum = 0;
 $sum += $_ foreach @result;
 $sum += $offset if $sign eq '+';
 $sum = $offset if $sign eq '';
 $sum *= $offset if ($sign eq '*'  $sign eq 'x');
 do { $sum /= $offset; $sum = int $sum; } if $sign eq '/';

+ my $sum = 0;
+ $sum += $_ foreach @throws;
+ (my $expr = $mod) =~ tr/Xx/**/;
+ $sum = int eval "$sum $expr" if $expr;
return $sum;
}
Update: Looking at this node again, I realized that the patch would break the b syntax, and so I, uh, fixed that. I also trimmed the original author's code a bit.
