Quick Add Reference extension by Clarius Consulting lets you quickly add a missing reference for a type in C# code. When you use a new type and Visual Studio 2010 asks are you missing an assembly reference, in the correction options popup menu you now have the item to add the reference:

Add reference menu item in Visual Studio 2010 correction options popup menu

Selecting the Add Reference menu item adds the reference and adds the necessary using statement:

PresentationCore assembly reference and using System.Windows statement added by the Quick Add Reference extension

To open the correction options popup menu in Visual Studio 2010 you can hover the mouse over the help button or press Ctrl + . (Ctrl and dot). The same add reference menu item is available in the Error List tool window for the assembly not referenced error:

Add reference menu item in the build error description context menu

The Quick Add Reference extension learns about types and corresponding assemblies as you add them using the standard Add Reference dialog. Once you’ve added an assembly manually, Quick Add Reference remembers it and in the future will offer you an option to add it via the popup menu.

The free Quick Add Reference extension supports only Visual Studio 2010 and C# language. You can download it from the Visual Studio Gallery.