There are plenty of software applications and services available to monitor servers alerting you if you have a problem. But none of them come close to the awesomeness of this traffic light server monitoring system which has been created using a little Arduino wizardry.
The monitor has been created to work along side xymon in this instance and provide a simple overview for the most critical systems.
Depending on the components you already have lying around you might be able to scrap the bits together. The main working stop lights was purchased for $199 and components ran to around $130. If you fancy building your very own all instructions and the components you will need are listed over on the Instructables website.