I have a couple of pair of "Noise Buster Extreme" headphones that we
use on airplane flights and which I use when riding the bus. They
allow the use of a feedthrough audio signal (airline garbage audio
or walkman) as well. They do a good job on low frequencies, better
than 10 dB attenuation. It is dramatic to sit in my kitchen, switch
the 'phones on, and hear the refrigerator drone vanish! They are
made in China, and my local drugstore remaindered them at C$20/pair.
I bought their last four pair after spending C$50 on my first pair.
That was Christmas of 1998, and I haven't seen them since. They were
in a plastic blister pack. (I've given the other three pair away to
children and a friend.)