A few sites I'm proud to have worked on include:
(There are a lot more listed on my resumé.)
Sisyphus is a figure in Greek mythology. He committed a crime against the gods--different accounts tell of different crimes, but all the stories agree he was not a particularly honorable fellow in his life. He's best known for his afterlife, though; he was condemned to an eternity at hard, frustrating labor. In the realm of the dead, he is forced to roll a great boulder to the top of a steep hill. Every time Sisyphus, through his excruciating toil, gets the rock to the summit, the darn thing rolls back down and the whole process starts again--lasting all eternity.
"Sisyphean" refers to something that's both extremely effortful and futile. Like keeping this Website up-to-date, for example.