…are now available to MSDN subscribers here. (These will be available to non-subscribers on October 21.) The official product launch date is March 22, 2010. Here’s the official press release with many more details about the product lineup, etc.
Also released today is the latest Silverlight Toolkit for Silverlight 3. You can read about changes made between the Silverlight Toolkit July 2009 release and the Silverlight Toolkit October 2009 release here.