IPC -The Association Connecting Electronics Industries. They set the standards we manufacture to. 

PCB007 – real-time magazine providing PCB informations for readers around the world.

CadSoft - offers solutions for PCB design, including Schematic Capture, Board Layout, and Autorouter. 

Everything PCB - Printed Circuit Industry product, service and resource guide. 

PCBLibraries - Land pattern calculators/tools/libraries, other resources, online forums. 

PCB Café -A PCB portal. It's got technical papers, book reviews, software announcements, and a comprehensive news feed.

Electronics Lab- useful circuits with full description,  diagrams and PCB, electronics articles, links and downloads.

SMTnet - provide the most efficient and effective two-way exchange between providers and users of the products, services, and information related to electronics manufacturing. 

Webopedia - the number one online encyclopedia and search engine dedicated to computer technology.

Circuit World - Circuit World Online Services, the leading provider of information and commercial services to Electronics Manufacturing.