A new virtual lab that I don't think I've mentioned was posted a while ago on MSDN. The lab covers exposing a WCF service using REST, as well as covering communicating with JSON in WCF.

REST, AJAX, and Web 2.0 in Windows Communication Framework

Here are the previous virtual labs that have been published as well for WCF.

Building AJAX/JSON Services using WCF

Syndication using Windows Communications Foundation

A Server Scenario Lab with Windows Communication Foundation

Understanding Windows Communication Foundation

The Fundamentals of Programming the Windows Communication Foundation

Reliable and Transacted Messaging with the Windows Communication Foundation