PowerCommands for Visual Studio 2008. Install it. Nothing else really needs to be said, but I want to highlight a few things.
This is a free Microsoft built VSX (Visual Studio Extensibility) extension. It adds extremely useful yet simple menu commands that are integrated as if Visual Studio shipped with them already there. I will not go into the detail of the commands there is a comprehensive yet brief document here for that. It is definitely worth the installation and Visual Studio just does not feel the same without it anymore.
I have been using version 1 for a couple of months now and have just found version 1.1 was released a month ago which adds a host of new handy features. It gets better, the source code is available. This provides a great example on how to code seamless add-ins to Visual Studio. Before you can build the source you need to install the Visual Studio SDK. I have a list of simple refactoring commands that I intend to write as a learning exercise that will also make common coding tasks easier.
If PowerCommands has convinced you that free first party VSX extensions are a good thing, be sure to check out other releases from Microsoft on the Visual Studio Gallery. The Resource Refactoring Tool is another very good must have.