"TIMTOWTDI"

My 2 ¢:

use warnings;
use strict;
use feature qw(say);
sub zip;

say zip 'ABCDEFGHIJ', 'abcde';

sub zip {
    join "", sort { lc $a cmp lc $b } split "", $_[0] . $_[1];
}

__END__
[download]

I guess it's slower than some of the examples above but it doesn't look bad ;-)

And i learned something. See Strange Observation [SOLVED] for details. Thanks to toolic, KurtSchwind, Athanasius and some unknown soldier.

Update: Same benchmark as used by BrowserUK:

karls-mac-mini:monks karl$ ./benchzip.pl 
         Rate    B Karl    A    C
B     98641/s   -- -17% -44% -68%
Karl 118153/s  20%   -- -33% -62%
A    176987/s  79%  50%   -- -43%
C    312785/s 217% 165%  77%   --
[download]

Regards, Karl