<p>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.</p>

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