Screen savers aren't exactly in vogue these days thanks to a shift in thinking towards turning off a display rather than leaving it on constantly displaying photos. If you can't resist a screen saver, however, try this minimalist Mac 'saver.
It's designed by Robert Padbury, formerly of Apple fame, and displays either a black on white digital clock which takes up your whole screen, or a white on black arrangement. It's fabulously minimalist, and it's my new favourite screen saver. [Clock]