One contest that was really big around the late 80's was The Secret Sound Contest. A caller had to guess what the sound was.
If the answer wasn't right, the jackpot would increase. The sounds could be anything from a pulley being pulled to a car door closing. Some of them were really tough. The station that orginally did it was K-LITE 94, which is no longer on the air. Another station did it for a brief period, however I can't remember which one it was.