RHQ has a little known plugin called the "netservices" plugin. Someone was asking about how RHQ can monitor HTTP endpoints on the #rhq freenode chat room - you use this netservices plugin to do this.
There are actually two different resource types that plugin provides - one allows you to monitor an HTTP URL endpoint (e.g. so you can monitor for different HTTP status codes). The other is a very basic resource type that just verifies that you can ping a specific IP or hostname.
Here's the RHQ 4.5.1 version of that plugin and its source:
(note: if anyone in the community is interested in doing some work on RHQ and looking for something simple to do - here's a perfect opportunity. It would be nice to have some documentation written for that plugin, but more importantly, I think we could beef up this plugin. For example, it would be nice to have another resource type (similar to that basic PingService) that is able to confirm that a particular port on a particular IP/host can be connected to. We also could use some testing done on this plugin to make sure it still works as expected.)