Web developers who would like to use CSS3 intellisense in Visual Studio 2010 can download this for free as an add-on form this website. Make sure you close VS before running the installer. The file should be automatically installed to C:\Program Files\Microsoft Visual Studio 10.0\Common7\Packages\1033\schemas\CSS .
Open up VS again and open a CSS file. You should be able to pick CSS3 from the style sheet toolbar. If not you should run the following registry script (don't forget to close VS before running the script):
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\10.0\Packages\{A764E895-518D-11d2-9A89-00C04F79EFC3}\Schemas\Schema 5]
"File"="css30.xml"
"Friendly Name"="CSS 3.0"
Open VS again and everything should work.
Happy CSS-ing.