Great article by Breman Sinaga at http://www.codeproject.com/
Breman explains common design patterns by a Storage Explorer sample application:
Introduction: "A lot of information about GoF design patterns has been published, however most of the examples use separate illustration for each pattern, and the sample code is not an application with a real function. The Storage Explorer is a small application that is designed to use several design patterns together. While the main purpose of this submission is to share the code than to teach the reader about design patterns, the discussion about the application design itself is explained using design patterns.
This article discusses the structure of the application, the design patterns that I use, how it works and the advantages of using them. In my opinion design pattern is worth learning. Developers who have design pattern skill can recognize the intent of a program and the purpose by identifying the patterns. The classes with complex relations then can be understood better and faster than if the developers only understand basic OO design. The design patterns can be used as a thinking model for the designer and the code reader.
The application is used to explore file composition inside a computer storage. The design patterns that are used are: Strategy, Observer, Adapter, Template Method, Singleton and Wrapper Façade. The first five are known as GoF design patterns and the last one is a POSA pattern (POSA book volume-2).