Just been having a play with a cool new "beta" feature from CopperEgg, it's called Servers Map.
I strongly suggest those who are interested give it try. Great tool for understanding what's talking to what within your infrastructure (and your web application).
For those of you not familiar with CopperEgg, they are a "Cloud Computing Systems Management" company. There products mostly fall into the SaaS category with monthly subscription payment models.
CopperEgg requires a small agent to be installed on the servers or instances you wish to monitor. You get an API key which links each agent to your account.
As soon as the agent is installed, literately seconds later, your CopperEgg dashboard lights up with some fantastic information.
There are heaps of other features so I won't go into them all, the usual suspects are there, including alerting, reporting, dashboard etc. I'm definitely becoming a big fan.
You can register for a free 13 day trial of CopperEgg and it's excellent monitoring service @ www.copperegg.com.
Definitely worth a butchers hook.
Here is a sample of the output that you can get from Servers Map. Shows which services and applications are using what ports to communicate with other stuff both on you local network and the outside world.