I’ve been creating one for my development team by combining parts of all the good / great ones that I’ve been able to find. Here are links to the ones I am using…
Microsoft – Design Guidelines for Class Library Developers – http://msdn.microsoft.com/en-us/library/ms229042.aspx
IDesign C# Coding Standard – http://www.idesign.net/idesign/download/IDesign CSharp Coding Standard.zip
SubMain C# / VB.NET Coding Guidelines – http://submain.com/products/guidelines.aspx
Lance Hunt – C# Coding Standards – http://weblogs.asp.net/lhunt/archive/2004/08/17/CSharpCodingStandardsv113.aspx
DotNetSpider – C# Coding Standards and Best Programming Practices – http://www.dotnetspider.com/tutorials/BestPractices.aspx
Microsoft – C# Programming Guide – http://msdn.microsoft.com/en-us/library/67ef8sbd.aspx
Phillips Medical Systems – Coding Standard C# – http://www.tiobe.com/content/paperinfo/gemrcsharpcs.pdf