From the asp.net blog.

"Today we shipped the final release of Silverlight 2.  You can download Silverlight 2, as well the Visual Studio 2008 and Expression Blend 2 tool support to target it, here.

Cross Platform / Cross Browser .NET Development

Silverlight 2 is a cross-platform browser plugin that enables rich media experiences and .NET RIAs (Rich Internet Applications) within the browser.

Silverlight 2 is small in size (4.6MB) and takes only 4-10 seconds to install on a machine that doesn't already have it.  It does not require the .NET Framework to be installed on a computer to run - the Silverlight setup download includes everything necessary to play video or run applications.

Developers can write Silverlight applications using any .NET language (including VB, C#, JavaScript, IronPython and IronRuby).  Silverlight provides a rich set of features for development including:

• WPF UI Framework: Silverlight 2 includes a rich UI framework that makes building rich Web applications much easier.  In includes a powerful graphics and animation engine, as well as rich support for higher-level UI capabilities like controls, layout management, data-binding, styles, and template skinning.  The WPF UI Framework in Silverlight is a compatible subset of the WPF UI Framework features in the full .NET Framework, and enables developers to re-use skills, controls, code and content to build both rich cross browser web applications, as well as rich desktop Windows applications.

• Rich Controls: Silverlight 2 includes a rich set of built-in controls that developers and designers can use to quickly build applications.  The Silverlight 2 release includes core form controls (TextBox, CheckBox, RadioButton, ComboBox, etc), built-in layout management panels (StackPanel, Grid, Panel, etc), common functionality controls (Slider, ScrollViewer, Calendar, DatePicker, etc), and data manipulation controls (DataGrid, ListBox, etc).  All Silverlight controls support a rich control templating model, which enables developers and designers to collaborate together to build highly polished solutions.

• Rich Networking Support: Silverlight 2 includes rich networking support.  It includes out of the box support for calling REST, WS*/SOAP, POX, RSS, and standard HTTP services.  It supports cross domain network access (enabling Silverlight clients to directly access resources and data from resources on the web).  It also includes built-in sockets networking support.

• Rich Base Class Library: Silverlight 2 includes a rich .NET base class library of functionality (collections, IO, generics, threading, globalization, XML, local storage, etc).  It includes rich APIs that enable HTML DOM/JavaScript integration with .NET code.  It includes LINQ and LINQ to XML library support (enabling easy transformation and querying of data), as well as local data caching and storage support.  The .NET APIs in Silverlight are a compatible subset of the full .NET Framework.

• Rich Media Support: Silverlight 2 includes built-in video codecs for playing high definition video, as well as for streaming it over the web (including both live and on-demand support).  Silverlight includes support for adaptively switching video bitrates on the fly based on network conditions (enabling users to avoid seeing the dreaded "buffering..." message), placing and metering ads within video streams, as well as enabling content protection. 

The final Silverlight 2 release delivers a tremendous amount of power and flexibility that enables you to really push the boundaries of what can be done in a browser, and enable great end user experiences."

Read more: http://weblogs.asp.net/scottgu/archive/2008/10/14/silverlight-2-released.aspx