Conky is a system monitor for X originally based on the torsmo code. Since it's original conception, Conky has changed a fair bit from it's predecessor. Conky can display just about anything, either on your root desktop or in it's own window. Conky has many built-in objects, as well as the ability to execute programs and scripts, then display the output from stdout.
WWW: http://conky.sourceforge.net/