The Shabbos before Tisha B'Av gets a very sad Haftorah, known as Chazon. It's Isaiah 1:1--27. (I recommend you open the text in a new window, or else the answers to this question will make no sense.)
Tradition has it that most of it is chanted with the extra-sad tune used for Lamentations (Eicha), instead of the usual Haftorah tune. But which parts? Is there an official source on this? Is it still a matter of local custom? Or even individual preference?