At this moment I'm diving into Design Patterns and Business Objects.  Later I will blog more about these items, but now I just put down the resources I have at this moment:

• First of all: Microsoft Patterns & Practices Developer Center 
• Basic article about Design Patterns: http://msdn.microsoft.com/msdnmag/issues/01/07/patterns/
• Great .Net examples can be found @ Data & Object Factory.  It includes the GoF patterns in C#, Service Oriented Architecture Design Patterns, The Head First Design Patterns converted from Java to .Net and more
• About the prototyping Design Pattern 
• LHotka site with a great example CSLA.Net

I also have bought a few books:

• Head First Design Patterns (Eric & Elisabeth Freeman), which I'm reading now.  This book has it's examples in Java, but that should be no problem.
• Expert C#2005 Business Objects (Rockford LHotka)

At the project I'm working this moment, we are using Design Patterns like the state Machine Pattern.  We have created a base business object based on LHotka.  We have included the rule manager for broken rules of LHotka.  At last we also included the use of property bags (-Collections).  We have prepared the base in the first project.  All of this will be extended during the next projects.  We have seen that we have the need for some extensions, but have chosen for the pragmatic approach (also because of the project deadline ).