NameDomainLink
Wikipedia Lists 

http://en.wikipedia.org/wiki/Metadata_standards
http://en.wikipedia.org/wiki/Ontology_%28information_science%29

Dublin Core http://dublincore.org/
FOAF  
EML 

http://im.lternet.edu/sites/im.lternet.edu/files/emlHandbook.pdf

FGDC geospatial metadata http://www.fgdc.gov/metadata/geospatial-metadata-standards
OGC metadata specification (adopted from ISO 19115) http://www.iso.org/iso/catalogue_detail?csnumber=26020
OGC Observation & Measure specification (metadata is part of it) http://www.opengeospatial.org/standards/om
OGC SensorML (metadata is part of it) http://www.opengeospatial.org/standards/sensorml
OGC WaterML (metadata is part of it) http://www.opengeospatial.org/standards/waterml
Earthcube metadata research (good short description) http://api.ning.com/files/fQeo9nzhJbkjXQgugGqsCwQ04djjIHp3iVpXJb5NKYrK5KGHJpX8CfFhiUnI6tQQTq*38M3IDt91YfxDJpxhXj1xSEnTMYsE/1116resubMetadataEOIFinal.pdf
CIDOCCultural Heritagehttp://www.cidoc-crm.org/