You could try something like this:

#! perl -slw
use strict;
use List::Util qw[ sum ];

our $N ||= 9;

#my @data = ( 9,1,1,1,1,1,1,1,1,1 );
my @data = map{ int rand( $N ) } 1 .. $N;

my @a = @data[ 0 .. $#data / 2 ];
my @b = @data[ $#data / 2 + 1 .. $#data ];

my $diff = abs( sum( @a ) - sum( @b ) );

print "$diff : [@a] [@b]";

OUTER: for my $ai ( 0 .. $#a ) {
    for my $bi ( 0 .. $#b ) {
        if( abs(
            sum( @a[ 0 .. $ai-1, $ai+1 .. $#a ], $b[ $bi ] )
          - sum( @b[ 0 .. $bi-1, $bi+1 .. $#b ], $a[ $ai ] )
          ) < $diff
        ) {
            my $temp = $a[ $ai ];
            $a[ $ai ] = $b[ $bi ];
            $b[ $bi ] = $temp;
            $diff = abs( sum( @a ) - sum( @b ) );
            print "$diff : [@a] [@b]";
            last OUTER if $diff == 0;
        }
    }
}
[download]

It could be coded more efficiently and I haven't yet convinced myself that it will always find the optimum solution, but it seems to get pretty close quite quickly even for quite large arrays:

C:\test>junk -N=25
13 : [6 8 12 19 12 16 19 2 14 2 12 18 2] [3 23 24 7 11 7 16 10 6 6 12 
+4]
7 : [3 8 12 19 12 16 19 2 14 2 12 18 2] [6 23 24 7 11 7 16 10 6 6 12 4
+]
3 : [3 6 12 19 12 16 19 2 14 2 12 18 2] [8 23 24 7 11 7 16 10 6 6 12 4
+]
1 : [3 4 12 19 12 16 19 2 14 2 12 18 2] [8 23 24 7 11 7 16 10 6 6 12 6
+]

C:\test>junk -N=25
64 : [11 11 22 2 19 17 17 10 6 20 17 5 20] [21 21 0 12 4 3 8 22 0 6 13
+ 3]
42 : [0 11 22 2 19 17 17 10 6 20 17 5 20] [21 21 11 12 4 3 8 22 0 6 13
+ 3]
28 : [0 4 22 2 19 17 17 10 6 20 17 5 20] [21 21 11 12 11 3 8 22 0 6 13
+ 3]
26 : [0 3 22 2 19 17 17 10 6 20 17 5 20] [21 21 11 12 11 4 8 22 0 6 13
+ 3]
20 : [0 0 22 2 19 17 17 10 6 20 17 5 20] [21 21 11 12 11 4 8 22 3 6 13
+ 3]
18 : [0 0 21 2 19 17 17 10 6 20 17 5 20] [22 21 11 12 11 4 8 22 3 6 13
+ 3]
2 : [0 0 11 2 19 17 17 10 6 20 17 5 20] [22 21 21 12 11 4 8 22 3 6 13 
+3]
0 : [0 0 12 2 19 17 17 10 6 20 17 5 20] [22 21 21 11 11 4 8 22 3 6 13 
+3]

C:\test>junk -N=25
80 : [10 9 23 4 14 22 0 17 19 9 16 24 24] [20 20 7 4 7 13 0 5 5 10 20 
+0]
74 : [7 9 23 4 14 22 0 17 19 9 16 24 24] [20 20 10 4 7 13 0 5 5 10 20 
+0]
68 : [4 9 23 4 14 22 0 17 19 9 16 24 24] [20 20 10 7 7 13 0 5 5 10 20 
+0]
60 : [0 9 23 4 14 22 0 17 19 9 16 24 24] [20 20 10 7 7 13 4 5 5 10 20 
+0]
56 : [0 7 23 4 14 22 0 17 19 9 16 24 24] [20 20 10 9 7 13 4 5 5 10 20 
+0]
50 : [0 4 23 4 14 22 0 17 19 9 16 24 24] [20 20 10 9 7 13 7 5 5 10 20 
+0]
42 : [0 0 23 4 14 22 0 17 19 9 16 24 24] [20 20 10 9 7 13 7 5 5 10 20 
+4]
36 : [0 0 20 4 14 22 0 17 19 9 16 24 24] [23 20 10 9 7 13 7 5 5 10 20 
+4]
16 : [0 0 10 4 14 22 0 17 19 9 16 24 24] [23 20 20 9 7 13 7 5 5 10 20 
+4]
14 : [0 0 9 4 14 22 0 17 19 9 16 24 24] [23 20 20 10 7 13 7 5 5 10 20 
+4]
10 : [0 0 7 4 14 22 0 17 19 9 16 24 24] [23 20 20 10 9 13 7 5 5 10 20 
+4]
6 : [0 0 5 4 14 22 0 17 19 9 16 24 24] [23 20 20 10 9 13 7 7 5 10 20 4
+]
4 : [0 0 4 4 14 22 0 17 19 9 16 24 24] [23 20 20 10 9 13 7 7 5 10 20 5
+]
2 : [0 0 4 4 13 22 0 17 19 9 16 24 24] [23 20 20 10 9 14 7 7 5 10 20 5
+]
0 : [0 0 4 4 13 22 0 17 19 9 16 23 24] [24 20 20 10 9 14 7 7 5 10 20 5
+]

C:\test>junk -N=25
43 : [22 10 14 1 2 1 16 8 19 20 17 24 21] [13 23 2 2 19 1 21 12 1 6 22
+ 10]
25 : [13 10 14 1 2 1 16 8 19 20 17 24 21] [22 23 2 2 19 1 21 12 1 6 22
+ 10]
3 : [2 10 14 1 2 1 16 8 19 20 17 24 21] [22 23 13 2 19 1 21 12 1 6 22 
+10]
1 : [1 10 14 1 2 1 16 8 19 20 17 24 21] [22 23 13 2 19 2 21 12 1 6 22 
+10]
[download]