Best space themed screensaver ever, isn't really a screensaver at all.
The free open source Stellarium
can be launched as a 'screensaver' with the small IdleStart
utility I made.
Just set IdleStart to load at startup with a shortcut in the Startup folder. In that shortcut, set the parameters for length of idle time and path to Stellarium.
Now you have the space screensaver to beat all.