• MARC21
• UniMARC
• CDWA
• XML
• Dublin Core
• Unicode
• OpenURL
• OAI-PMH
• Z39.50
• SRU/SRW
• NCIP
• Dublin Core, Simple Dublin Core
  
• IEEE LOM (Learning Objects Meta-Data) - http://ltsc.ieee.org/wg12/20020612-Final-LOM-Draft.html
• 
  

See also http://www.bibliothecarium.org/