VisualVM - All-in-One Java Troubleshooting Tool
VisualVM is a new graphical troubleshooting tool that is being developed in a project on java.net. It gives access to the functionality that is available through existing JDK tools such as JConsole, jinfo, and jstack, and adds to that support for lightweight profiling of CPU and memory usage.
These screenshots from the project page give an idea of what the tool can do.
The tool is extensible via downloadable plugins, and the latest milestone publishes an API for developing your own plugins. Also, if you have developed plugins using the JConsole Plugin API it's possible to use them unchanged in VisualVM.
I'm not personally involved in this project but I'm certainly following it with great interest.