A little afternoon golf produced this scary looking solution... It assumes the elements in the array are unique (i.e. a set) and none of them contain the comma character.

#!/usr/bin/perl -wT
use strict;

my @a    = 1..5;
my $l    = 3;
local $" = ',';

my @combos = grep!$;{"@$_"}++,map[sortsplit','],
             grep!/([^,]+).*,\1,/,glob"{@a},"x$l;

print "@$_\n" for @combos;

__END__
1,2,3
1,2,4
1,2,5
1,3,4
1,3,5
1,4,5
2,3,4
2,3,5
2,4,5
3,4,5
[download]

Update: There is a subtle bug in the second line of the golfed statement... grep!/([^,]+).*,\1,/ is supposed to filter out all permutations that have doubled elements, but its a bit faulty. It doesn't affect the final value of @combos though. Anyone want to take a guess at it? Whats the bug, and why doesn't it matter in the end?

-Blake