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).

Learn how to create an encrypted sparse disk image that mounts and unmounts on login/logout. With symbolic links in the proper places, Mail, Address Book, and iCal are none the wiser, and you can be reasonably assured that your private data will stay secure.

Free open-source disk encryption software for Windows Vista/XP, Mac OS X, and Linux.