Casio watches and the G-Shock in particular are some of the most ubiquitous wristwatches in the world (see the Casio G-Shock GLX-150 review).
The brand can be found just about anywhere you look; in department stores, discount stores, online (of course) and -- yes -- even in wristwatch retail shops!
Just about everyone I've know or have talked to about wristwatches has owned a Casio at one time or another and often a low-end Casio digital watch will serve as a youngster's first "serious" timepiece.
Mechanical wristwatch fanciers may scoff at the brand but there's no denying that Casio has, in their own way, brought an appreciation of timekeeping to the masses and they have also developed a huge cult following for the very popular G-Shock.