Behavioral Design Patterns

Observer

Object (subject) maintains list of its dependencies (observers). Subject will then notify observers whenever any state change occurs in it. 

Related patterns are Publish-Subscribe pattern, mediator and singleton 
http://weblogs.asp.net/fmarguerie/events-references-garbage-collecting-memory-leaks-and-weak-delegates

Iterator

http://sourcemaking.com/design_patterns/iterator

Mediator

Defines an object which encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects referring from each other explicitly.

http://www.dofactory.com/net/mediator-design-pattern  
Template method
http://www.oodesign.com/template-method-pattern.html

Null object

Strategy

Defines set of algorithms that can be used interchangeably. Basically you create an interface and derive implementations from that. Clients can couple themselves with the interface. 

http://robdodson.me/javascript-design-patterns-strategy/
http://sourcemaking.com/design_patterns/strategy

Command

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