I've just posted up a review of AOpen's HP-590 "Vibration Bass" headphones. Here's a snippet from the review:

"AOpen has developed a very unique feature with their HP-590 headphones, dubbed "Vibration Bass." Basically, this pair of headphones features a second 30mm "vibration" driver that is specially designed to translate low frequency sounds into vibrations. This is designed to add to the overall audio sensation by accenting bass with a tactile response."

Read it here.