Pattern Library for Interaction Design

While creating a complicated form or multi-step Indicators or want to know different type of form validation or visual framework, its always interesting when we look at the pattern libraries used. Below are the list of website which has some nice collection of interaction patterns. For each pattern - get the answer on what?, when to use it?, why and how?

• Designing Interfaces - http://designinginterfaces.com/

• Yahoo! Design Pattern Library - http://developer.yahoo.com/ypatterns/index.php

• Welie - http://www.welie.com

• UI Patterns - http://ui-patterns.com/

• Interaction Design Pattern Library for Games - http://www.helpyouplay.com/

• Mobile User Interface Design Patterns http://patterns.littlespringsdesign.com/~newlsdpatterns/index.php/Main_Page
  This site is a wiki, with few patterns for handheld devices
  

• Web Patterns - A UC Berkeley Resources for Building User Interfaces
  http://groups.ischool.berkeley.edu/ui_designpatterns/webpatterns2/webpatterns/home.php