Official Silverlight 3 release - download links / urls
Silverlight 3 was released by Microsoft yesterday and here are the download links of the development tools, for future reference:
Expression Blend 3 with Sketchflow
Silverlight 3 Software Development Kit (SDK)
Silverlight 3 Tools for Visual Studio 2008 SP 1
these links go directly to the download page, so understand that they may become outdated after a few months.
For the actual Silverlight runtime, you can download the latest version here: http://www.microsoft.com/silverlight/resources/install.aspx