Checkstyle for C#?

What you're looking for is called Static Code Analysis.

FxCop is one option. I think Resharper can check this kind of thing as well.

Take a look at resharper.

Have you tried StyleCop?

• http://code.msdn.microsoft.com/sourceanalysis

Note: This's been moved to https://github.com/StyleCop

We use StyleCop to enforce our coding standards. It is free and integrates nicely with Visual Studio