Design Patterns

Design patterns are recurring solutions to software design problems you find again and again in real-world application development. Patterns are about design and interaction of objects, as well as providing a communication platform concerning elegant, reusable solutions to commonly encountered programming challenges.
The Gang of Four (GoF) patterns are generally considered the foundation for all other patterns. They are categorized in three groups: Creational, Structural, and Behavioral. Here you will find information on these important patterns.
Creational Patterns
Abstract Factory Creates an instance of several families of classes.
Builder Separates object construction from its representation.
Factory Method Creates an instance of several derived classes.
Prototype A fully initialized instance to be copied or cloned.
Singleton A class of which only a single instance can exist.

Structural Patterns
Adapter Match interfaces of different classes.
Bridge Separates an object’s interface from its implementation.
Composite A tree structure of simple and composite objects.
Decorator Add responsibilities to objects dynamically.
Facade A single class that represents an entire subsystem.
Flyweight A fine-grained instance used for efficient sharing.
Proxy An object representing another object.
Behavioral Patterns
Chain of Responsibility A way of passing a request between a chain of objects.
Command Encapsulate a command request as an object.
Interpreter A way to include language elements in a program.
Iterator Sequentially access the elements of a collection.
Mediator Defines simplified communication between classes.
Memento Capture and restore an object's internal state.
Observer A way of notifying change to a number of classes.
State Alter an object's behavior when its state changes.
Strategy Encapsulates an algorithm inside a class.
Template Method Defer the exact steps of an algorithm to a subclass.
Visitor Defines a new operation to a class without change.
Suggested Books:
Design Patterns: C#3.0 Design Patterns By Judith Bishop O’REILLY
Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley)
Suggested Link: http://www.dofactory.com/Patterns/Patterns.aspx