Three great Wikipedia pages I found today:

http://en.wikipedia.org/wiki/Fictitious_entry: "The salesman is put on trial for treason, but reveals that the encyclopedia article for the star system... is a fictitious entry included in the encyclopedia to detect plagiarism..."
http://en.wikipedia.org/wiki/Bielefeld_Conspiracy: "the [Bielefeld] city council released a press statement titled Bielefeld gibt es doch! (Bielefeld does exist!)..."
http://en.wikipedia.org/wiki/Clinamen