A Guide to Supply Chain Management

• Institute for Supply Management (ISM)  
    
  Founded in 1915; one of the largest trade organizations for the field. There are some useful, and even some free (non-member), items in their Tools area. 
  They produce the Report on Business (includes the PMI), a major barometer of business activity that is regularly quoted in the news.
• American Society of Transportation & Logistics
• American Trucking Associations
• APQC (American Productivity & Quality Center)
  An organization for process and performance improvement. Helped establish the Malcolm Baldridge Quality Award.
• Association for Operations Management (APICS)
• Chartered Institute of Purchasing & Supply
  A UK trade association.
• Council of Supply Chain Management Professionals
• International Federation of Purchasing & Supply Management
  A union of 48 national and regional purchasing associations worldwide.
• National Purchasing Institute
  "An association of government purchasing professionals."
• Project Management Institute
• Supply Chain Council

• Glossary of Supply Chain Terms
  From Inbound Logistics.
• Quality Dictionary and Glossary
  From iSixSigma.com.
• Supply Chain Management Definition and Solutions
  From CIO Magazine.
• Supply Chain Management Terms & Glossary
  From the Council of Supply Chain Management Professionals.

• Healthcare Purchasing News
• Inside Supply Management
  From the ISM. Not free, unfortunately ...
• Logistics Management
• Supply Chain Digest
  A helpful site: look at the Resources/Education tab for case studies, white papers, and more.
• Supply Chain Management Review
• SupplyChainBrain
• World Trade

This is a very selective list, obviously!  For a complete list, use the A - Z listing from USA.gov.