Where can I find a good collection of public domain owl ontologies for various domains?

I am building an ontology-processing tool and need lots of examples of various owl ontologies, as people are building and using them in the real world. I'm not talking about foundational ontologies such as Cyc, I'm talking about smaller, domain-specific ones.

From stackoverflow Kevin Pauli

• There's no definitive collection afaik, but these links all have useful collections of OWL and RDFS ontologies:

  • schemaweb.info
  • vocab.org
  • owlseek
  • linking open data constellation
  • RDF schema registry (rather old now)

  In addition, there are some general-purpose RDF/RDFS/OWL search engines you may find helpful:

  • sindice
  • swoogle

  Ian

  From Ian Dickinson

• Thanks! A couple more I found:

  • OntoSelect - browsable ontology repository
  • Protege Ontology Library
  • CO-ODE Ontologies
  From Kevin Pauli

• One more concept search tool: falcons

  From Ian Dickinson

• Within the life-science domain, the publically abvailable ontologies can be found listed on the OBO Foundry site. These ontologies can be queried via the ontology lookup service or the NCBO's Bioportal, which also contains additional resources.

  From fgibson

• There is also one good web engine for searching for ontologies. It is called Watson Semantic Web Search and you can try it here.

  From Bakhtiyor