Silverlight 5 has just been released. You can download the developer runtime (32-bit or 64-bit), Silverlight Tools for Visual Studio including the SDK and Silverlight toolkit here and start creating Silverlight 5 applications.
There are many online learning resources of Silverlight. You can find some of them here.
One of the new features of Silverlight 5 is its support for 3D with GPU acceleration. You can view a live example (Babylon 3D Engine) hosted on Windows Azure and download its source code here. Note: The Silverlight Toolkit comes with a number of demos. See a description of the demos here.