I also like the Sennheiser HD600s. I use them with a Headroom Cosmic. The Headroom gear has the option of allowing you to have the signal processed so it sounds more natural, less like it is resolving along the plane of your head. Many people also recommended to me the Grado RA-1, though I have never heard it. You could get the Senns and a used Grado amp within your budget.
If you stretch your budget a bit, you could get a used Stax tube or solid state headphone amplifier and earspeakers. The more expensive earspeakers offer better bass. In the older lineup, the signatures were better than the professionals and the professionals better than whatever the standard model was called. You can check out the current lineup at http://www.stax.co.jp/ENG/products.html. These models and the older models appear on Audiogon and Ebay from time to time, some of the olders models even at your specified price. A good set of earspeakers will give you better sound and are even more comfortable than the HD600s.
If you stretch your budget a bit, you could get a used Stax tube or solid state headphone amplifier and earspeakers. The more expensive earspeakers offer better bass. In the older lineup, the signatures were better than the professionals and the professionals better than whatever the standard model was called. You can check out the current lineup at http://www.stax.co.jp/ENG/products.html. These models and the older models appear on Audiogon and Ebay from time to time, some of the olders models even at your specified price. A good set of earspeakers will give you better sound and are even more comfortable than the HD600s.