My favorite is the horrendously expensive MIT speaker and interconnect cables that have their "mystery electronics" in little boxes at the ends. So people spend a couple grand (yes...thousands) for a pair of MIT Oracle speaker cables to use them as fancy tone controls for their speakers. 8-)

Unfortunately, the cable/interconnect business is chock full of manufacturers who make dubious claims and then spend lots of money throwing ads in the various audio/theater rags. And editors/readers lap it right up....

Cheers,