StyleCop helps you maintain a particular style and consistency in how you format and write the source code in your .NET Assemblies, Frameworks, and Reusable Libraries.
JetBrains ReSharper is a Visual Studio Add-in that provides refactoring, code analysis, and other features to make your developer experience more productive.
The StyleCop Plugin for ReSharper allows you to maintain source code style consistency as you type in Visual Studio, giving you the best of ReSharper and StyleCop.
"StyleCop for ReSharper" is a ReSharper 4.1 plugin that allows Microsoft StyleCop to be run as you type, generating real-time syntax highlighting of violations. StyleCop for ReSharper can now be published thanks to the release of the StyleCop 4.3 SDK."
Learn more here.