Port forwarding with xinetd - this is really useful. I spent ages trying and failing to get an iptables-based forward from an IP address/port on machine 1 to an IP address/port on a remote machine2. I thought about writing some sick Python to forward incoming connections, but running it as root to bind the right port/IP or doing yet more iptables didn't appeal ... and then I remembered this is what xinetd is for.

So on Debian, you can apt-get install xinetd and use the config above to forward arbitrary ports (there's also a 'bind' directive to specify the IP to bind to on the forwarding machine).