If you find a good resource on JSR 168 portlets on the web, please include a link here.
PortletSwap.com Maintained by JBoss, features JBoss Portal portlets and layouts.
Java.net Portlet Community Although a bit disappointing, some of the resources are pretty darned good.
Project PortletMVC Home Development of JSR 168 compliant portlets based on MVC pattern
MVC WebWork Portlet Framework MVC Framework for JSR168 Portlet based on WebWork,Velocity, Spring, Hibernate.
Project portletUnit jUnit Java Unit Testing Framework for testing JSR-168 portlets
Spring PortletMVC provides a complete MVC layer for the JSR-168 Portlet API in the same way that Spring WebMVC does for the Servlet API.
Caucho JSR 168 Tutorials A variety of Portlet tutorials
Osmond's Portlet Utilities IPC and some portlets that should assist in testing
Article - Developing to the Java Portlet Specification Article describes coding a QueryPortlet that displays the contents of a database query.
Project Kosmos Open source JSR-168 portlets for software project monitoring