The last time I dealed with "Screenlets". Screenlets are little gadgets, how they are known from Windows Vista/7.
I found a very nice application for Linux. If you have Ubuntu 9.10, you can go to the software centre and search for "Screenlets".
After installing you can find the application under applications -> accessory -> screenlets.
There you will find gadgets for hardware monitoring and many more.
Here you can download useful Screenlets: