You may have heard the old joke--there are only ten types of people in the world: those who know binary, and those who don't. Well, use this LED Binary Watch from ThinkGeek to see whether those jokesters really do know what they're talking about. The watch has ten blue LEDs that indicate the binary sequence (1, 2, 4, 8, 16, 32), and you add up the lit LEDs to determine the time. The numbers are labeled, however, which makes it a little easier.
ThinkGeek | $55