The DCMI Metadata Terms lists the current set of the 15 elements from the Dublin Core metadata schema. In addition, more qualified terms are added to this schema, which acts to refine certain fields of the schema for greater description. The full list of terms can be found at http://dublincore.org/documents/dcmi-terms/.
Darwin Core is a body of standards primarily based on taxa, their occurrence in nature as documented by observations, specimens, samples, and related information. The Simple Darwin Core is a specification for one particular way to use the terms - to share data about taxa and their occurrences in a simply structured way - and is usually what is meant if someone suggests to "format your data according to Darwin Core." There is also another format of Darwin Core that includes more terms for auxiliary terminology.
You can find the documentation for Simple Darwin Core at http://rs.tdwg.org/dwc/terms/simple/index.htm.
Darwin Core terms are found at http://rs.tdwg.org/dwc/terms/.
The Global Information Locator Service defines a core element set for government information so that it can be more searchable and discoverable by the general public. Details can be found at: http://www.archives.gov/records-mgmt/policy/gils.html.
Categories for the Description of Works of Art (CDWA): A conceptual framework and guidelines for the description of art objects and images. Its site is at http://www.getty.edu/research/publications/electronic_publications/cdwa/index.html.
MPEG-7: The Multimedia Content Description Interface MPEG-7 is an ISO/IEC standard and specifies a set of descriptors to describe various types of multimedia information and is developed by the Moving Picture Experts Group. It is available at http://mpeg.chiariglione.org/standards/mpeg-7/mpeg-7.htm.
NISO Metadata for Digital Images: This standard defines a set of metadata elements for faster digital images to enable users to develop, exchange, and interpret digital image files. The dictionary has been designed to facilitate interoperability between systems, services, and software as well as to support the long-term management of and continuing access to digital image collections. For details, please refer to http://www.niso.org/apps/group_public/project/details.php?project_id=69Visual.
Visual Resources Association Core Categories (VRA): a data standard for the description of works of visual culture as well as the images that document them. Its website is at http://www.loc.gov/standards/vracore/.
PBCore: the metadata standard for audiovisual media developed by the public broadcasting community. Its official website is at http://pbcore.org/index.php.