Updated version for 2016 here!
Conky is a free, light-weight system monitor for X that can display a wealth of information from Linux. Unfortunately (to some) it is a bit tedious to configure as it's based on a resource/text file. I do really like having it on my desktop though, so that didn't stop me.
After spending more time than I probably should have, I came up with this (based on this):
I've put it on Github to ease updates, but you can also download the file directly below. To use it, simply copy the .conkyrc file into your home directory (~/). Note that the CPU Type is hardcoded, as Conky can't seem to read that parameter. Simply put whatever text you'd like in that area (it's commented in the file).
» Get it on Github
#Protip - if you're using Compiz and have Conky startup automatically, you may notice that it starts to appear on top of all other windows. Luckily, there's an easy fix. Hope you enjoy it!