The Code Project has some very readable samples for the GOF Design Patterns:
Illustrated GOF Design Patterns in C#.
Part I: Creational (Abstract Factory, Factory Method,
and Builder)
Part II: Structural I (Adapter, Bridge, Composite, and
Decorator)
Part III: Structural II (Facade, Flyweight, and Proxy)
Part IV: Behavioral I (Chain of Responsibility,
Command, and Interpreter)
Part V: Behavioral II (Iterator, Mediator, Memento,
Observer, and State)
Part VI: Behavioral III (Strategy, Template Method,
and Visitor)
Alex van Buitenen, feb 2007.