Use the ancient xfishtank toy with some mods to gnome to have animated fishies actually swimming around in the root window.
Several simple mods to gnome are required to let this work.
*System Tools > Apps > Nautilus > Preferences - uncheck show_desktop.
* Downlaod xfishtank via apt
* for some reason, the xfishtank flag to draw a background image wont work, so you will have to put "display -window root aquarium.jpg" as a preferences > sessions > startup item
* Put xfishtank as a startup item as well in there.
* get rid of the stupid top gnome panel bar (it can all fit in one panel anyway)
* conky for system information (this will work now in gnome again given that we have regained control of the root window)
the fish actually swim over the conky panels, and under the gdesklet panels (as shown in the screenshot). very relaxing. cpu usage - minimal.
if you like it, please vote 'good'
now if only we could get better fish images...