Buffalo Ontology Site  
   Information on ontology, on the history of ontology, and on contemporary ontology and its applications.
   http://wings.buffalo.edu/philosophy/ontology/

Stanford Encyclopedia of Philosophy: The Identity of Indiscernibles  
   A principle of analytic ontology first explicitly formulated by Leibniz. It states that no two distinct substances exactly resemble each other.
   http://plato.stanford.edu/entries/identity-indiscernible/

Stanford Encyclopedia of Philosophy: Tropes  
   An article describing tropes; by John Bacon.
   http://plato.stanford.edu/entries/tropes/

Descriptive and Formal Ontology  
   An extensive resource site on the development of ontology, especially in the twentieth century.
   http://www.formalontology.it/

Stanford Encyclopedia of Philosophy: Holes  
   An interesting case-study for ontologists and epistemologists.
   http://plato.stanford.edu/entries/holes/

Stanford Encyclopedia of Philosophy: Events  
   Survey of philosophical views on the character and status of events; by Roberto Casati and Achille Varzi.
   http://plato.stanford.edu/entries/events/

Stanford Encyclopedia of Philosophy: Physicalism  
   Discussion of the thesis that everything is physical; by Daniel Stoljar.
   http://plato.stanford.edu/entries/physicalism/

Stanford Encyclopedia of Philosophy: Abstract Objects  
   Survey of attempts to draw the distinction between concrete and abstract objects; by Gideon Rosen.
   http://plato.stanford.edu/entries/abstract-objects/

Qualia: The Knowledge Argument  
   Aims to establish that conscious experience involves non-physical properties. It is one of the most discussed arguments against physicalism; from the Stanford Encyclopedia by Martine Nida-Rümelin.
   http://plato.stanford.edu/entries/qualia-knowledge/

What is Ontology?  
   Collected definitions, from leading philosophical reference works and from philosophers from Wolff to Husserl.
   http://www.formalontology.it/section_4.htm

Why Does Anything Exist?  
   Sequence of short essays on this topic.
   http://www.hedweb.com/nihilism/

Metaphysics of Quality  
   Robert M. Pirsig deals with the fundamentals of existence and attempts to provide a more coherent system for understanding reality than current paradigms allow.
   http://www.moq.org/

Stanford Encyclopedia of Philosophy: Existence  
   Survey article by Barry Miller.
   http://plato.stanford.edu/entries/existence/

The Metaphysics of Blue  
   On the nature of consciousness - looking for soul in a soulless world.
   http://www.geocities.com/Athens/Acropolis/5243/

The Shift of Aspect in Language and Thought  
   Notes on the relational element in the assertion that things exist. Patterned on Wittgenstein's Philosophical Investigations.
   http://mysite.wanadoo-members.co.uk/salt/