As a developer I always look for some utilities that can help raise my productivity bar and avoid common bugs. I always go for open-source projects and free software first, cause we all know that in many cases we have a very limited budget to invest. So here is some GREAT pieces of software that can help you.
A very good tool for code analysis, your code will be checked against a wide rage of rule sets that cover almost everything. It can be integrated with Visual Studio 2008.
Microsoft StyleCop (http://blogs.msdn.com/sourceanalysis/)
StyleCop analyzes C# source code to enforce a set of style and consistency rules, it can be integrated and run directly inside Visual Studio.
PowerCommands for Visual Studio 2008 (http://code.msdn.microsoft.com/PowerCommands)
It is a set of useful extensions for the Visual Studio 2008 adding additional functionality to various areas of the IDE.
CodeRush Xpress (http://devexpress.com/Products/Visual_Studio_Add-in/CodeRushX/)
A free refactoring tool for C# language with limited functionalities that integrates a the default refactoring features exposed by Visual Studio 2008. It cannot be used with Visual Studio Express.
Refactor! for Visual Basic (http://devexpress.com/Products/Visual_Studio_Add-in/VBRefactor/)
A free refactoring tool for Visual Basic .NET, it cannot be used with Visual Studio Express.
Refactor! for ASP.NET (http://devexpress.com/Products/Visual_Studio_Add-in/RefactorASP/)
A free refactoring tool for ASP.NET, it cannot be used with Visual Studio Express.
Note that CodeRush Xpress, Refactor! for Visual Basic and Refactor! for ASP.NET are limited versions of full products and they cannot be installed together, so you have to choose and use the one that matches best your actual developing environment.