I wrote about VisualVM yesterday (entry) but I had missed Octavian's Introduction where he gives instructions on how to use VisualVM on MacOS X.

As a reminder, to run the VisualVM client you need a recent JVM, so you will need to use the latest JVM from Apple, but the app can run in a variety of JVMs, remote or local to VisualVM. VisualVM can even save the data into a snapshot and process it offline.