I think this thread needs some Sony MDR-CD900ST love.
They are my gold standard for the human voice. Not a single headphone, open or closed, has a better mid range. Or, rather, no other headphone comes as close to sounding like a live singer as these do. Some people might like a more energetic mid range, or a warmer mid range, so I guess I shouldn't say they have "the best" mid range, but as far as a true-to-life sound, they are just the tops.
They don't have the bass that most closed headphones have (my old AKG K271's were bass monsters in comparison), but these aren't meant to be an "every" headphone. They are pretty much exclusively for folk, lighter rock (folk rock, soft rock, maybe some prog rock, those sorts), and tracking voices in the studio. They sound a little dull for anything else, but for those genres, they are absolutely a top-tier headphone.
Isolation isn't so great, and the fact that they only come with a 1/4" adapter limits their use outside the home/studio. Still, they are closed, and do offer some isolation!
Oh, and speaking of AKG K271's, how great are they? On the used market they are like $75, and to my ears, are easily comparable to the Sennheiser HD-25's and Beyerdynamic DT1350's.
EDIT: I really need to find a local Head-fi meet to bring the CD900ST's to. I'm starting to sound like a broken record, and giving the CD900ST's a chance to tell their story might bring them from relative obscurity.
Edited by Kukuk - 9/10/12 at 7:09am