In the wake of the recent internet traffic monitoring law passed in Sweden, it is highly overdue to get serious about encryption. First off, e-mail encryption, focusing on PGP/GPG. Below are a some useful links:

Enigmail: PGP/GPG extension for Mozilla Thunderbird.

FireGPG: GPG extension for Mozilla Firefox. Brings e-mail encryption to Gmail, and any other website with GPG content.

GpgOL is a plugin for Microsoft Outlook 2003, by the maintainers of GnuPG.

GPGoe is a GPG plug-in for the Microsoft Outlook Express.

For even more links about PGP/GPG and related tools, see Folkert van Heusden's collection of information.