I guess I'm the only one who voted "other". I've broken one thermometer, but the one that gets me is tubing.
Due to the relative positioning of the important, necessary features in my kitchen (i.e., stove, sink, electrical outlets), I have managed to melt holes in (and thus perform emergency repairs on) my tubing at least 5 times while trying to chill the wort. In fact on my last two batches in a row I melted the damned tubing. I am thinking about making a new wort chiller with really long intakes/outlets so I can keep the tubing as far away from the pot as possible in the future.