NuGet package. The package contains the Silverlight and the Windows Phone binaries. The sources and the PDB are also available at SymbolSource.org.
NuGet is a neat package management system for the .Net platform which makes the life of a .Net developer much easier. If you haven't tried NuGet until now, you should definitely give it a try. I'm sure you won't regret it. To install NuGet, open Visual Studio's Tools -> Extension Manager and search the Online Gallery for NuGet. You can then open a project, right click the References and select "Add Library Package Reference".