OPC Foundation
Official source for OPC-related news and resources
http://www.opcfoundation.org/

OPC Council Japan (in English)
OLE for Process Control Technical Outline and an extensive glossary of OPC terms
http://www.opcjapan.org/eng/index.asp

OPC Europe
A calendar of OPC events and seminars
http://www.opceurope.org/

Programmer's Connection
An independent Web site dedicated to the needs of OPC developers
http://www.opcconnect.com

Control Magazine
A monthly magazine serving the needs of automation, control, and instrumentation professionals in the process industries
http://www.controlmagazine.com