I own several pairs of the Sony MDR-7506, which are my #1 reference headphone. I love them except they don't isolate outside sounds as well as I'd like for live concert tracking. This lead me to try out some other headphones.
The problem I have with most headphones -- even very expensive "pro" models -- is very uneven midrange, and a ~250 Hz resonance that makes the mid-bass sound muddy. I tried Beyerdynamic DT770 Pro (80 ohm version), Ultrasone models (seriously disappointing), and Shure's $99 cans (truly horrible sounding -- why would they put their name on that??).
Then I alighted upon the ATH-M50S. They are larger than the Sony headphones, more comfortable, more isolating, and sound almost as good!
These headphones are great to listen to, as they have a fuller mid-bass than the Sony (too full for accuracy, but nice to listen to), and a bit more of a relaxed upper-mid. When switching between these and the Sonys, the Sonys started sounding peaky and harsh in the upper mids. The Audio Technicas, to my ears, actually sound better with classical/symphonic material. The sound is very pleasing. When I show a mix off to someone using my MP3 player, I had them these headphones rather than the Sony... It gives them that "wow" factor.
These are a very worthy headphone, with good isolation, a nice, heavy-duty plug and plug adapter... Scratch that, the whole headset is rugged!