I'm surprised this one has never caught on. I imagine it's only due to a lack of people taking the time to let others know of it. So here it is..
This utility integrates a command prompt window within explorer that stays synchronized with the folder you're viewing in explorer. It includes macro support which is a wonderful extension to the command prompt.
It works through some API hooks combined with normal shell extension interfaces. For the most part, it works well. This project could use a new maintainer though. It doesn't work under x64 at the moment, it needs some modifications in the API hooking code.
Download and source code: http://www.codeproject.com/csharp/CommandBar.asp