I like my devices to be fast and having a screensaver of any type seems to slow things down so I don't have any of them but if I did it would probably be something with nature.
A pause from Screensavers! to share interesting fact from antiquity:
Today is: 23rd September (GMT), in history on the 23rd of September, 1955 AD the following event happened:
Yanks clinch pennant by beating Red Sox, 3-2