Google Fools' Day
Since 2000, Google has published one or more gags every year except 2001 and 2003.
Not only are they usually entertaining, but the yearly ritual has turned into a big marketing ploy for the company.
This year, there is a spate of articles on news sites and blogs about the possible upcoming gag, or even whether the ubiquitous company will do one since the national mood may not be up for a gag in the midst of a recession.
All this adds up to a ton of free publicity for Google, as if they needed it.