For Dedicated or VPS customers:
In your
WHM > cPanel > Addon Modules you will find a new add-on at the bottom called Munin. You might be interested in installing it. It is a nice graph based monitoring tool that monitors all sorts of goodies like cpu load, memory load, swap load, mailman usage, exim load, over a period of day, week, month, year.
This is a live demo:
http://munin.ping.uio.no
A screenshot is attached of how to reach the install area.