WCF RIA Services - You can download a version of RIA Services for either Visual Studio 2010 or 2008. This is also a great page to find sample code, walk-throughs, videos, forums, etc for RIA Services. This is a great starting point.
Below are some links to some more advanced RIA Services topics.
Silverlight 3 and RIA Services - The advanced things – Several interesting advanced topics
Walkthrough: Creating a RIA Services Class Library – If you have a Web Site instead of a Web Application, you may want to look at this since Web Sites can’t be linked to RIA Services. This serves as a nice workaround though and allows for reuse, which is very nice.
How to: Add or Remove a RIA Services Link – Nice if you want to change your RIA Services Link
WCF RIA Services Code Gallery – a good place to get source code for the walk-throughs.