If the keys really are like your example (one upper case letter followed by one or more numbers), you're in luck - sort will do what you want right out of the box (just try it).

Err, um, not quite:

use strict;
use warnings;

my @array = qw(a1 a10 a100 a11 b2 b10 b200 b25);

print 'bobf sort: ', join ' ', sort @array;
print "\n  GF sort: ", join ' ', sort alfNum @array;

sub alfNum {
    my ($aAlf, $aNum) = $a =~ /([a-z]+)(\d+)/i;
    my ($bAlf, $bNum) = $b =~ /([a-z]+)(\d+)/i;
   
    return $aAlf cmp $bAlf if $aAlf ne $bAlf;
    return $aNum <=> $bNum;
}
[download]

Prints:

bobf sort: a1 a10 a100 a11 b10 b2 b200 b25
  GF sort: a1 a10 a11 a100 b2 b10 b25 b200
[download]