One of the sessions of TheServerSide Java Symposium in Prague was about JMX support in Java. During the talk Jean Francoise Denise briefly demoed a new tool VisualVM based on the Netbeans Platform. Today I did some experiments and found it quite useful. It is also utilizing the NetBeans plugin mechanisms to provide extensibility (e.g in order to monitor JMX Beans you must install the MBeans plugin).
The tool even provides a profiler. I haven’t even looked at it closer. Though I believe it is quite useful to have it available for ad doc profiling without requiring any external tools!