Moo0 SystemMonitor is an application that displays various system statistics right on your desktop. It has a large variety of sensors like CPU usage per core, free memory, hard drive temperature, incoming and outgoing bandwidth and much much more. It doesn't use too many system resources (ive noticed on 2 server systems and 1 client system that it uses around 20MB of memory and between 0.20% to 1.3% CPU). It's an especially useful application to use on a server since you can monitor everything going on in one central location. You can change skins, increase/decrease the font size, change transparency, dock it, auto hide it, change the layout and more.
You can download Moo0 SystemMonitor from http://www.moo0.com/software/SystemMonitor/ Moo0 SystemMonitor is freeware and is compatible with Windows XP/2003/Vista