UI pattern

Usually, most of us as designer needs to find a UI control or widget or pattern to do a job in a software or website. We end up looking for various controls from different website or software's or OS etc. The major confusion we have is what to use and when to use a particulars control, widget or pattern.

Here are links to few website that had solved and given answers to most of the common questions that we have:
http://ui-patterns.com/
http://developer.yahoo.com/ypatterns/index.php
http://patterntap.com/

For example, lets say we are thinking about calender control and why and when to use. We can easily follow these 2 links to find calender controls and there implementation in different websites:
http://developer.yahoo.com/ypatterns/pattern.php?pattern=calendar
http://patterntap.com/tap/ (click Collections > Select Calendards and then click Filter)
http://www.welie.com/patterns/showPattern.php?patternID=event-calendar
http://interface.fh-potsdam.de/infodesignpatterns/patterndetail.php?pattern=97

So, the result shows various calender controls used in different websites and what problem does that design element solves.