Can I add a Windows Explorer context menu option to start command prompt in the selected directory?

Right-click on the folder itself with Shift held down, and a new context item should appear named Open command window here.

This trick also works if you do it in the empty space of a folder.

1. Start / Run / regedit

2. Navigate to the following keys in turn:

   HKEY_CLASSES_ROOT\Drive\shell\cmd
   HKEY_CLASSES_ROOT\Directory\shell\cmd
   HKEY_CLASSES_ROOT\Directory\Background\shell\cmd
   

3. Under each in the right pane you'll see a REG_SZ string value called Extended. Just rename this to something else (in case you want to easily undo the change) or delete it (just that value):

   

4. Now you can simply right-click a drive or directory and have the Command Prompt option show up without having to press Shift.

Just type "cmd" in Windows Explorer's address bar.