I bought the Sennheiser HD 600 about seven years ago for evening listening and digital music recording, without compromising audio quality. They were retailing at 250GBP when I bought them and they have now dropped in price to about 160GBP. They were worth 250GBP. I have a midrange audio setup (Arcam Alpha 8R, Alpha 8SE etc.) and they bring out the best in it. If you have a reasonable system then these give open, airy and truly reference quality sound reproduction.

I have a pretty high end system, consisting of Musical Fidelity components and B & W speakers, with a Rega headphone amp, and I am completely blown away by the Sennheiser HD 600 headphones every time I listen through them. I audition all my kit a lot, and these were far and away the best for sensible-ish money!

They are definitely an at home headphone though - unless you like the marble-esque Cyber Man look. I don't think anyone would feel comfortable walking down the street in them, and the open back design makes them bleed too much noise to be usable on trains and planes.

If you want a reference headphone, then buy them while you still can. I prefer them to the 650's, and you can get a good price if you hunt around.