I have just released a number of plugins, mostly for monitoring OSS
software here:
https://github.com/genman/rhq-plugins
Some of them are a bit rough around the edges, but most have been in
use for many years at my company.
The most significant one, I think, is the SNMP plugin, which can
generate a working plugin descriptor for any device that has a MIB.
Included are plugin descriptors for Citrix Netscaler, Fusion-io, and
NetApp filer generated by the plugin. Obviously cleaning up the
descriptor may be required in some cases.
For the full list:
https://github.com/genman/rhq-plugins/blob/master/README.md