Add IntelliSense for CSS Selectors
Can you add IntelliSense support for CSS selectors in stylesheets?
You can autocomplete all HTML tag names, all pseudo-classes (preferably with parameter hints) and pseudo-elements, and all IDs and classes that appear in other selectors in that or other stylesheets.
This is now included in Visual Studio 2013 Update 2 and 3
The Web Essentials 2012 extension now does this.