How do I manage multiple audio playback devices on Windows Vista/7?

The solution to all your nagging Windows automation problems: AutoIt!

Put this AutoIt and compile it

;-----Configuration-----
;The title of the sound config window.
Dim $ConfigWindowTitle = "Sound"
;-----End of configuration----

Dim $ItemNumber = 1
If $CmdLine[0] >= 1 Then ;If we have a parameter...
    $ItemNumber = $CmdLine[1] ;...we should press the button the specified number of times.
EndIf

Run("control mmsys.cpl") ;Run the sound control applet and hide it.

WinWaitActive($ConfigWindowTitle) ;Wait for it to be active before sending keystrokes.

Send("{TAB}{TAB}{TAB}{TAB}") ;Put the focus on the list

For $i = 1 to $ItemNumber Step 1
    Send("{DOWN}")
Next

Send("!s") ;Press Alt + S to set the selected device as the default.
WinClose($ConfigWindowTitle)

Now create a shortcut, and in the Target put the path to the compiled executable. For an argument, put the number of the sound device in the list that you want to switch to. (to switch to the top item in the list, put 1, the second item in the list, put 2, etc). If you want a keyboard shortcut, use the Shortcut Key field in the shortcut's properties window.

I'd been looking for something to do what you wanted to do, and found that there's no programmatic way that you can switch audio devices in Vista/7. It's just not something that Microsoft decided that programmers need to do, so I make this script to automate the process. It's not the best since it pops up the window in order to change the device (necessary), but it makes it possible to create shortcuts to change the output device for your sound.

Default Audio Changer is currently the best solution, in my opinion.

It uses undocumented system calls instead of simulating keyboard presses, which means you can use it in fullscreen applications without worry.

@Dan Walker Nice solution, but not perfect ;)

This script uses the existence of a file to actually perform a toggle, so you can use the same shortcut to switch between playback devices. It's just a simple edit:

;-----Configuration-----
;The title of the sound config window.
Dim $ConfigWindowTitle = "Sound"
;-----End of configuration----

Dim $ItemNumber = 1 ; The first itme in the audio list

If FileExists ("a") Then; Use the existence of a file to know if we should toggle
    FileDelete("a")
    $ItemNumber = 3 ; The audio playback device you want to toggle to
Else
    FileOpen("a", 1)
    FileClose("a")
EndIf

Run("control mmsys.cpl") ;Run the sound control applet and hide it.

WinWaitActive($ConfigWindowTitle) ;Wait for it to be active before sending keystrokes.

Send("{TAB}{TAB}{TAB}{TAB}") ;Put the focus on the list

For $i = 1 to $ItemNumber Step 1
    Send("{DOWN}")
Next

Send("!s") ;Press Alt + S to set the selected device as the default.
WinClose($ConfigWindowTitle)