Performance tuning your java and j2ee applications
Visual VM in JDK 1.6 is one of the best tools for monitoring the performance of your java/j2ee application. I am not sure why Sun has not marketed it well and kep it secret but this is a very good options for developers who always wanted to see how their applications behaves and if there are bottlenecks.
Imagine a developer did some change in application (added a new feature) and would like to know how his changes impact the application. Visual VM is very helpful in these situation. You can use it with standalone java application and can also integrate with your server.
Some of the helpful links on Visual VM are
Visual VM – All in one trouble shooting tool

