Well, JBoss is probably doing a lot of caching internally but other than that, there's at least a couple of ways: 1) Let Hibernate cache your data (docs) 2) Use the JBoss TreeCache MBean (docs)
If you're clustering jboss and looking for high throughput and HA (e.g. BetFair) then check out Coherence.
Peace.
<a href="http://www.tangosol.com/" target="_blank" rel="nofollow">Tangosol, Inc.</a><br /><a href="http://www.tangosol.com/coherence.jsp" target="_blank" rel="nofollow">Coherence</a>: Easily share live data across a cluster!