Patterns patterns on the Wall, which is the Coolest of them All
The Observer Pattern.
Its easily the coolest and most practical pattern I have ever used and since I am big fan of DRY (Don’t Repeat Yourself), I will redirect you to an article which I recently wrote on CodeProject about the Observer pattern.
Implement Observer Pattern in .NET (3 techniques)
The above link has different techniques (along with source code) of implementing Observer pattern in .NET using C#.
It explains the various libraries provided by Microsoft in successive versions of .NET framework in order to implement the Observer Pattern.
The Observer pattern a.k.a Publisher-Subscriber pattern is the one to which you can actually relate in the real world.
Hope its an interesting read.