I recently did a question and his answer was a pattern called Attached Behavior, now instead of asking how to do something every time, it would be better to ask Where I can find a list of design patterns available?.
“available” is a big term. what I look for are patterns available for application development in WPF, C# .NET3.5/4.0/4.5 technologies, if possible explained with examples and beyond the more common.
Costs $79 but well worth it IMHO: http://www.dofactory.com/Framework/Framework.aspx
It is very extensive, has the GoF and Head First, Enterprise patterns and many more, contains real-world examples and also more abstact examples and includes sourcecode for each-and-every pattern contained in the “package”. And ofcourse it is targetted at .Net (as per your question) but is applicable to every other capable language.
Although the quality is not extremely high, it does offer good value for money IMHO.