Factory Method Pattern

The factory method pattern is an object-oriented design pattern. Like other creational patterns, it deals with the problem of creating objects (products) without specifying the exact class of object that will be created. The factory method design pattern handles this problem by defining a separate method for creating the objects, whose subclasses can then override to specify the derived type of product that will be created. More generally, the term factory method is often used to refer to any method whose main purpose is creation of objects.

http://en.wikipedia.org/wiki/Factory_method_pattern

http://lennilobel.wordpress.com/2009/08/06/leveraging-polymorphism-with-factory-classes/

http://dofactory.com/Patterns/PatternFactory.aspx