It’s ‘data about the data’ and it’s vital to GIS. Tools, extensions and tutorials on how to accurately document your data.

ANZLIC
Australian lead standard of core metadata elements for Australia and New Zealand.

Federal Geographic Data Committee
The Federal Geographic Data Committee (FGDC) develops geospatial data standards for implementing the National Spatial Data Infrastructure, in consultation and cooperation with State, local, and tribal governments, the private sector and academic community, and, to the extent feasible, the international community. The FGDC is committed to using voluntary consensus standards, such as those developed through ISO and ANSI. The FGDC also tracks other standards activities that may not be considered as voluntary consensus standards.

Metadata-L
The main objective of this list is to provide the GIS community with an open forum to share ideas and discuss metadata issues and strategies

National States GIC
A primer on what metadata is and how to use it by the National States Geographic Information Council (GIC).

NBII
Standards available for downloading for the National Biological Information Infrastructure.

USGS Metadata FAQ
FAQ compiled by Peter Schweitzer of the USGS.

USGS Metadata Tool Page
Lists some metadata tools for download that comply with FGDC standards.