Where can I get premade ontologies?

Given that creating ontologies is a highly costly and time consuming endeavor, its useful to first look for organizations or groups that have released ontologies related to the knowledge domain you're interested in. Not only are these usually standarized ontologies you can use as framework to test your algorithms, but they also can be extended and improved to make even more robust data management tools.

Sharing is caring after all.
http://dublincore.org/

http://www.foaf-project.org/

http://www.opencyc.org/