JBoss AS Clustering Guide. The architecture and design of the clustering implementation is described in detail along with a description of advanced configuration parameters and features.
The JBossHA wiki page that has links to numerous other wikis and a couple of articles as well.
JGroups. JBoss AS Clustering is built on top of JGroups distributed messaging technology. Check out the great work Bela Ban has done to allow for the quick development of JBossClustering.
JBoss Cache. JBoss AS Clustering uses JBoss Cache for most distributed state management handling. Learn more about this excellent caching library, which is very useful outside of JBoss AS as well.
The Using JBoss Cache as a Hibernate Second Level Cache reference manual details the Hibernate/JBoss Cache integration used for clustered caching of entities in Hibernate 3.3+ and JBoss AS 5.
JBoss Optimizations 101 @ onJava.com. Describes some basic JBoss optimizations and, as part of the article, how to use and setup the distributed cache invalidation framework, integrated with the clustering framework.
Clustering with JBoss 3.0. In this OnJava.com article. Bill Burke and Sacha Labourey introduce JBoss 3.0 clustering features and configuration and give a high-level view of JBoss clustering architecture.
Clustering with JBoss/Jetty. In this OnJava.com article. Bill Burke walks through his experiences setting up a "cluster" of JBoss 2.4.x servers at Mercantec. How can you get clustering features from a supposedly non-clusterable application server?
Cisco's HTTP Loadbalancer. Cisco should really be paying JBoss for this little advertisement, but a hardware based HTTP LoadBalancer may be useful in your application's architecture.
Apache/Mod_jk/Tomcat HTTP Loadbalancer. Software based load-balancer.
JBoss Clustering Webinar. Matt Quinlan, Manager of Systems Engineering with JBoss Inc., will explain the implementation of clustering in JBoss and conduct a demonstration of instantaneous failover within a cluster.