Using SSH as a proxy server (to avoid your company’s/country’s [firewall]): SSH has a built in SOCKS proxy that you can use in any program that can run over a SOCKS proxy. This includes Firefox (really, all browsers), Thunderbird, Pidgin/Adium (as well as almost all other IM clients like Google Talk, AIM, etc) and a ton of other networking programs we all use. Using SSH with the -D flag lets you create a dynamic ssh tunnel that acts as a SOCKS proxy, and sends all your traffic from the endpoint of your SSH connection.

And a small collection of other SSH secrets that are [fun][useful][illegal] (delete as appropriate).