http://www.extremeheadphones.com/
They are ear protection and headphones in one. Perfect for placing microphones since you don't hear the "outside" sounds and you clearly hear what the microphone hears. I never track without them.
They have a very "flat" sound and they wouldn't be my first choice for recreational music listening, but they are a workhorse in the studio.
Other uses include drummers who have to hear a click track and anybody listening in a noisy live stage environment.