An extension that we released a little while back and have been getting feedback on is the Memory Monitor Extension.
You can install this provider by going to your Railo Server Administrator (e.g: http://localhost/railo-context/admin/server.cfm) and heading to the Extensions > Applications section
Once installed, this extension adds a new section in the Railo Server Administrator that allows you to inspect the memory of your SERVER, APPLICATION and SESSION scopes
Link in the Railo Server Admin section
The Memory Monitor extension is available for Railo 3.3.x but it will expire on June 1st 2012. Since it is a rather popular extension, we have decided to extend the evaluation period till September 2012 (when we will release Railo 4.0!). To make sure your installation doesn't doesn't expire, make sure that you update the application via the Railo Server Administrator.
From October 1st (when the trial expires) this extension will be available as a paid extension, which you will be able to purchase through the Extension Store at a very reasonable price (to be announced).
In addition this extension, as well as a number of other paid extensions, will all be part of the commercial version of Railo 4.0 which will also be available in September