Microsoft has released the Silverlight 5 Release Candidate today..

• Silverlight 5 RC Features
  A PDF describing the features in Silverlight 5 RC
• Visual Studio 2010 SP1
  Installs Visual Studio 2010 Service Pack 1
• Silverlight 5 RC Tools for Visual Studio 2010 SP1
  Installs add-on pack for VS 2010 SP1 to build Silverlight 5 apps
• Silverlight 5 RC Runtime for Windows
  Installs run-time libraries to run Silverlight 5 apps
• Silverlight 5 RC SDK
  Installs an SDK for developing Silverlight 5 apps
• All Silverlight Downloads

Things you may also need to download:

Add-on and pre-requisite files for Visual Studio 2010 Service Pack 1 to develop Silverlight 5 RC and Microsoft WCF RIA Services V1.0 SP2 RC applications

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=27220

Expression Blend 5 Preview for Silverlight 5 RC

Expression Blend Preview for Silverlight 5 provides support for creating Silverlight 5 and Silverlight 5 SketchFlow projects.

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=9503