<p>Has anyone found a plugin for Visual Studio to allow for PowerShell syntax highlighting or IntelliSense? If not, does anyone have any idea why not?  I keep hoping someone else with copious free time would have tackled this by now. I have hope since other folks have managed to take the limited documentation and build custom IntelliSense providers for other languages such as <a href="http://sentia.com.au/2008/05/i-love-haml-but-i.html" rel="noreferrer">NHaml</a>.</p>

<p>Edit: To clarify,I'm not looking for a list of IDEs that can be used to develop PowerShell . I spend 90% of my day in Visual Studio.  It already does a really good job of slicing and dicing code. That is the IDE I prefer to use to edit all text and code.  The lack of PowerShell syntax highlighting now that I work with PowerShell scripts is down right painful.</p>

I have not seen anything about Visual Studio  Intellisense for PowerShell scripts.
I recommend you to try some other tools like:
PowerTab
PowerGUI
Look this screen cast:
(source:
aaronlerch.com
)