The Binary Clock

http://www.game-ntz.com/anorphous/clock.html

This clock is much more importaint

http://www.chasebrown.com/olson.htm

This analogic one’s much nicer:

http://www.lares.dti.ne.jp/~yugo/storage/monocrafts_ver3/03/

You can buy a binary clock here: http://www.thinkgeek.com/cubegoodies/lights/59e0/

Is cool.
But not very useful.