Natural Kinds
Category Induction and Representation, Natural Kinds and Projectible Predicates, Properties
Logic and Formal Ontology
Article by Barry Smith discussing Husserl's Logical Investigations.
Logic and Sachverhalte
Article by Barry Smith, discussing a view of logic which sees it as the science of states of affairs (Sachverhalte).
Meaning and the Problem of Universals
Subtitled a `Kantian-Friesian approach', an article by Kelley L. Ross. A nice historical survey of the problem of universal, but a bit weak on particular theories (eg. Frege).