A number of new tutorials have been published on the IBM Developerworks Site, on creating JSR 168 Portlets, which allow you to implement inter-portlet communication, portlet service and WSRP portlets. Check out all these tuturials here.
Creating a JSR 168 portlet for use by diverse portals using Web Services for Remote Portlets
Creating and deploying a portlet service for IBM and JSR168 portlets
Implementing JSR 168 inter-portlet communication using Rational Application Developer V6.0 and WebSphere Portal V5.1