Very easily the best system monitoring app that exists for
Gnome. In addition to what is mentioned above, it can also monitor
SETI@home status and
Distributed.net status. Along with those, it also displays the time and date, and even the local
weather (using information from the
National Weather Service). To appease you even more, it has controls for mounting/unmounting disks,
XMMS, volume, and infinitely more things thanks to its plugin capabilities.
All of this is displayed in a vertical bar that uses screen space rather efficiently. This is appreciated for those of us who have enough trouble with a 640X480 monitor.