New Relic RPM
http://www.newrelic.com/

You write good code. But things can happen. How fast can you spot application performance problems-and their root causes? Don’t rely on log files to solve tough performance problems. With New Relic RPM, you can monitor 24×7, detect problems in real-time, drill down to find the causes, and continuously tune for high performance. You’ll find your slow queries and controllers. You’ll trace transactions in fine detail. Use their dashboards or create your own. Add as many users as you like. It’s only a two-minute installation. Get your app in shape by tuning and scaling. This has been added to Script Resources Subject Tracer™ Information Blog.