Silverlight 5 Release Candidate is now available from Microsoft. They just released the RC build to public. You will be able to download it freely from Microsoft Download Center.
In this post, I am going to share the link of the Silverlight 5 RC Tools for Visual Studio 2010. Download it and start building your application. Make sure that, it's not in "Go-Live" license, so you can't deploy the Silverlight applications build with this release to production. This build is just for the developers to give the developers a chance to test their applications before they release the final version.