Control.com Forum
www.control.com The Control.com discussion forum, the largest, worldwide, on-line community of controls and automation engineers, where thousands of engineers freely discuss the technical and business issues that matter to them.
The Puffin Projects
PuffinPLC.org A site for open-source PLC (programmable logic controller) projects and related links.
PLC Archive
The PLC Archive A Control.com user-managed community resource, where one can contribute or download PLC programming examples.