Here are the list of C# Coding Guidelines document
  1. Microsoft’s All-In-One Code Framework Coding Guideline
  2. Design Guidelines for Developing Class Libraries – New one for .NET Framework 4 - You can also find the above document for the earlier versions of Framework in MSDN .
  3. C# Coding Standards document by Lance Hunt – pretty old but should be useful
  4. Coding Guidelines for CSharp 3.0 and 4.0 by aviva Solutions - The downloads here includes the coding guidelines , Visual Studio 2010 rule sets and ReSharper 5 Code Style 
  5. Philips Healthcare – C# Coding Standard 
  6. Encodo C# Handbook
  7. .NET/SQL/TFS Code & Application Design by SSW - This includes not just for C# but also for SQL Server , Project Management etc .
  8. SharpDevelop C# Coding Style Guide 0.3 by Mike Kruegar
  9. C# Coding Guidelines by Validio Software
  10. The IDesign C# Coding Standard, for development guidelines and best practices
  11. C# Coding Guidelines by agamura
  12. C# Coding Standards and Best Programming Practices by DotnetSpider
  13. Book : Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries (2nd Edition)Microsoft .NET Books)

Do you use the documents anything else apart from the above one’s ? , feel free to add them in the comment section .