Web sites that play sound with them. Either audio files or MIDI files. They give you no warning and frequently play loud and/or obnoxious sounds. And they usually have nothing to do with the content of the offending page(s). Frequently I catch myself asking, “where the hell did that sound come from?” Obnoxious web designers out there, do me this favor: save the sounds for multimedia files. Or at least let us turn them off. Or at least give us warning. Or at the very least, try to use good sounds that contribute to the web page (is that even possible?).