Monitoring tools

Whilst many RHEL users have external monitoring (of various forms) in place, a common requirement is for a process monitoring which can in principle be lightweight. I have found "monit" (available in EPEL) to be great for such a task.

I wonder whether some other tools should be available more broadly; for example, Nagios and Cacti (both widely used) to my knowledge are only available on the RHEL5 HPC channel?