IO::Socket::INET. Here's a command line one for you, s/"/'/ and s/'/"/ on *nix as this is Win32 quoting ;-)

perl -MIO::Socket::INET -le "do{$s=IO::Socket::INET->new(PeerAddr=>'12
+7.0.0.1',PeerPort=>$_,Timeout=>1);print $s? $_.' OPEN' : $_.' CLOSED'
+}for ARGV[0]..$ARGV[1]" 1 1024
[download]

You should also check out the Perl Power Tools Project which has ported many of the popular *nix command line tools to Perl.