Strategy design pattern

Strip the changeable method in a class to a hierarchy class.
ie changing a 'has-a' relationship to an 'is-a' relationship
Introduction: http://www.youtube.com/watch?v=9n3gF39-trE
Overview : http://www.youtube.com/watch?v=F1841_llRSw&NR=1
Coding : http://www.youtube.com/watch?v=vYByr2u8gqk&feature=related
Execution: http://www.youtube.com/watch?v=mmiWFcjMTLw&feature=related

Design Patterns Study Session: Decorator Pattern

Here's an excellent description of the Decorator Pattern:
Usage of wrapper to extend the functionality of a class without modifying the original class.

Introduction : http://www.youtube.com/watch?v=Xk8durvtiys&feature=related
Overview http://www.youtube.com/watch?v=MI_qyfeRk8c&feature=related
Code: http://www.youtube.com/watch?v=HkOdDMePE4Q&feature=related
Executing http://www.youtube.com/watch?v=Ra-33SFHq6M&feature=related

Design Patterns in Automation

Peter Kartashov has an interesting blogpost on application of design patterns in test automation. http://at4qa.blogspot.com/2010/01/20-essential-design-patterns-for.html