Semantic Radar is a semantic metadata detector for Mozilla Firefox.
Available at Mozilla Add-ons site. It is a browser extension which inspects web pages for links to Semantic Web metadata and informs about presence of it by showing an icon in browser's status bar. Currently it supports RDF autodiscovery (SIOC, FOAF, DOAP and any type) and RDFa metadata detection.
New: Semantic Radar can now ping the Semantic Web Ping Service when metadata are detected. This allows for a community based discovery of the Semantic Web data.