Is there a C# equivalent of Sonar?
You can use the Code Analysis tools in Visual Studio.
Also, there are third party tools that include much of the same information. Much of what is reported by Sonar is output by AQTime's Static Profiler, for example.
I imagine that Team System would be about as close as you could get (in terms of a monolithic software management tool for .NET-based products).
The possibility of Visual Studio Team Foundation Server is apply certain rules for coding. But it takes some effort into TFS to ensure the quality insurance.
Sonar is now avalable for C# ! You can check out the wiki page here : http://docs.codehaus.org/display/SONAR/.Net+plugin I am one of the developer of the "dotnet sonar plugin", your feedback is welcomed.
Did you have a look at NDepend? The tool analyze C# and .NET code and comes with plenty of cool features to browse the analysis results. With NDepend you can make rules, you can compare 2 versions of the code base and you can harness more than 80 code metrics.
Also, the tool comes with several great visualization features like:
Dependency Graph:
Dependency Matrix:
Code metric visualization through treemaping: