Yeah, I highly recommend the ATH-M50 headphones- they are great!
I have the Sennheiser HD-280PRO headphones also, and the ATH-M50 cans are just better all the way around....more comfortable too. I do use them all the time when mixing, along with my monitor speakers. I think they give a pretty good representation of what's at the bottom octave in my mix.
I also have a set of Sennheiser HD-580 headphones which are just spectactular in the mids and highs, but unreliable for mix decisions in the lows. The HD-580s are the most comfortable headphones I've ever worn though; I can wear them for hours. I use them mostly for editing, and sometimes for tracking myself (when I am playing a MIDI instrument).
JV