A Survey of Metadata Registries

Characteristics of Metadata Registries
Standards and APIs
Registry Standards
Schema Languages and Formats
Access Standards and APIs
Registries
IEMSR
SchemaWeb
DCMI Registry
Metadata Online Registry (METeOR)
NSDL Metadata Registry
XML.org Registry
DoD Metadata Registry and Clearinghouse
Other Registries
Commercial Tools

http://dart.edu.au/workpackages/da/registries.html