Truecluster is a framework for robust scalable clustering with model selection.
It allows objective determination of the optimal number of clusters even for non-parametric cluster algorithms.
This problem has not been considered as solved for more than 50 years since R. L. Thorndike's funny publication: "Who belongs in the family?" (Psychometrika, 4:267-276, 1953).
Oehlschlägel, J. 2007. Truecluster: robust scalable clustering with model selection, available at arXiv.org.
Oehlschlägel, J. 2007. Truecluster matching, available at arXiv.org.