(via www.susegeek.com)
Conky is a free, light-weight system monitor for X, that displays any information on your desktop. Conky is licensed under the GPL and runs on Linux and BSD. Conky has more than 250 built in objects, including support for a plethora of OS stats (uname, uptime, CPU usage, mem usage, disk usage, “top” like process stats, and network monitoring, built in support for IMAP and POP3 and many popular music players (MPD, XMMS2, BMPx, Audacious).