Conky is a system monitor that can display just about anything, either on your root desktop or in its own window. Conky has many built-in objects, as well as the ability to execute external programs or scripts (either external or through built-in lua support).
This is a full conky with most compile options enabled:
X11, XDamage, XDBE, Xft, MPD, MOC, math, hddtemp, portmon, RSS, Weather, wireless, IBM, nvidia, eve-online, Imlib2, ALSA mixer, apcupsd, I/O stats, argb, Lua and the cairo and imlib2 lua bindings, Audacious, and XMMS2.
