Grr., I'd forgotten you can't reply to answers and have it be visible on the answer screen... Plus, this is only a mild (much shorter, tho) variation of another answer. *sigh*
We're doing ridiculous ways now? Then why not do this?
my $x;
my @a = qw(one two three);
print $_, ++$x<@a ? ", " : "\n" foreach @a;