For me, headphones are pretty much a piece of apparel at this point. I keep a coiled mess of iPod headphones in my courier bag whenever the outside world gets too noisy, and at home I've got various pairs for recording, drumming, etc. Listening to music in a great pair of headphones can completely change the way we experience a song; forget laughable laptop speakers, or even well-positioned studio monitors when compared to a true holophonic aural experience, which can only be conveyed by isolated signals reaching either ear simultaneously.
C5 Sound Inc., a New York-based production company, recently posted this great article on the history of stereo headphones. Written by Mark Schubin, it covers the storied past of an integral component to the iPod/iPhone generation. For anyone that has wondered how headphones have evolved from navy and pilot communication devices to gym apparel, the answers lie in this article.