A friend asked me some time ago whether I have any good document regarding coding conventions and guidlines for C# and overall .Net programming. I didn't have an answer then so I handed them the document I compiled from my old VB days as a team leader regarding code conventions. It would at least be a blueprint as to what was needed.
However, I found a useful resource on this today (courtesy of Ed Kaim).
This link in MSDN contains just about anything one could ask for (A little bit too much actually) in terms of guidelines, ranging from naming conventions through Error and Exception handling and forwarding and up to "Guidelines for Exposing Functionality to COM".
Pretty darn thorough, I'd say.