81 chars to recursively construct the 2d array (not including "sub f {}"):

sub f {
#234567890123456789012345678901234567890123456789012345678901234567890
+12345678901
my$x=my$i=pop;$x?([1..$x],map[(map$_+2*$x-1,reverse@$_),++$i],reverse 
+f($x-1)):()
}
[download]

The first argument is the dimension of the spiral.

## print "@$_\n" for f(5);
1 2 3 4 5
16 17 18 19 6
15 24 25 20 7
14 23 22 21 8
13 12 11 10 9
[download]

The recursive pattern is the following: An n x n spiral looks like this:

 +---------------+
 | 1 2 3 ...  n  |
 | +-------+ n+1 |
 | |       |  .  |
 | |  ***  |  .  |
 | |       |  .  |
 | +-------+ 2n-1|
 +---------------+
[download]

where the *** box is the (n-1) x (n-1) spiral, rotated 180 degrees and 2n-1 added to each component.

Update: oops, moved a reverse to the right spot (didn't affect char count).

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