The Indiana Philosophy Ontology (InPhO) Project creates a dynamic formal ontology for the discipline of philosophy. The site allows you to browse the taxonomy and search Stanford Encyclopedia of Philosophy, Noesis (this was a search engine for open access, academic philosophy on the Internet) and Google Scholar. The project is described in the 2007 Joint Conference on Digital Libraries (JCDL) paper (ACM) and FirstMonday article.
[Edited from Photomedia Forum post by T.Neugebauer from October 29, 2007]