The Security Self-Defense Project from the Electronic Frontier Foundation - "The Electronic Frontier Foundation (EFF) has created this Surveillance Self-Defense site to educate the American public about the law and technology of government surveillance in the United States, providing the information and tools necessary to evaluate the threat of surveillance and take appropriate steps to defend against it." A comprehensive guide covering many types of surveilance and security technologoies.
Communication Security - another great resource covering many security and privacy topics, this one from Riseup.
Security In-A-Box - A set of how-tos and hands-on guides created to meet the digital security and privacy needs of advocates and human rights defenders.
Little Brother - full text of the book by Cory Doctorow; the whole book includes a lot of great tech and security information, but Chapter 10 has a good plain-English explanation of key encryption and key signing parties.
HTTPS Everywhere- free plugin for Firefox and Chrome that automatically uses HTTPS for many major websites, helping you browse securely more easily.
Tor - Free software that protects your privacy and anonymity online. Includes downloads, a live CD/USB distribution, how-tos and other resources.
Enigmail - a free security extension for the (also free) Mozilla Thunderbird email client that allows you to easily use GPG to encrypt and sign your email. You must also install GPG on your computer; downloads are available for Windows and Mac (Linux users, use your native package manager to install GPG if it's mot installed already.)