FXCop is code analysis tool that checks managed code assemblies for conformance to Microsoft's .NET Framework design guidelines. It allows you to customise the rules that are applied, so that you can add you own best practices and verify that you code always has the same quality throughout.
It been out for a while now, I think it was originally released around 2002? I'll have to check?
If you haven't used it before, you can download it for free at http://www.gotdotnet.com/team/fxcop.
The 1.3 version of FXCop has just been released, it had it has a new analysis engine.
After you have downloaded it and ran it against some of your project. Have a look at the June edition of the MSDN magazine, this article gives a good overview of the tool, how its works and some tips on how to use it.