Try http://www.head-fi.org - you will get better advice on headphones and associated gear there. It is unquestionably the reference headphone site. With your price range you have many, many options.
That said, personally I'd start with the Sennheiser HD-650s. I've owned these, and while they have a somewhat laid back presentation, they are absolutely magical with a first rate source. They can be had for around $350 new on ebay. I think I would also try a Grace 901 headphone amp, which can be had used for around $900 or less. (Don't worry about the 902 unless you need the upgraded DAC, as the headphone amp circuitry is essentially unchanged between the two). That leaves plenty of money for Cardis or Zu Mobius replacement cables for the 650s. Only your ears can tell you which you will find better, but you can buy them both (especially used) and sell the one you don't like as well with little or no loss.
