About.com VPN directory: A smattering of VPN resources including a glossary and a self-test.
Corecom VPN FAQ Page: Geared towards those new to VPN.
Find VPN: Directory of VPN providers, articles, and links.
How Stuff Works: How Virtual Private Networks Work: Gives definition of VPN and an overview of general VPN topics, includes diagrams and an animation.
NW Fusion: Research: VPNs: This is a comprehensive collection of VPN resources and articles.
Tom Dunigan's Virtual Private Networks page: This page describes IP-based VPN technology over the Internet
Virtual Private Network Consortium: VPNC is the international trade association for manufacturers in the VPN market.
VPN Info on the World Wide Web: All-encompasing guide to VPN. Includes standards, reviews, legal information, and howtos.
VPN labs - research community: VPN labs is an open community for researching, reviewing, and discussing Virtual Private Networks.