I'm in exactly the same situation as the OP (although I have set myself a budget, of up to £90).
For me, the ATH-M50 will probably be the way to go, considering that what I've read about the sound, both of the M50 and audio-technica generally, seems impressive (coming from my Sennheiser HD485, the more forward treble and mids should be suited to my tastes). There's also the fact that the M50 is IMO stylish enough to be used on the move and very well-built (some people have voiced concerns about breaking headbands, but that issue seems limited to the ATH-PRO700 - I've read lots of complaints about broken PRO700s on Amazon etc., but nothing about the M50. Besides, the construction of the troublesome area - where the cups attach to the headband - seems to differ between the two models).
Other headphones that I've read about and considered for this purpose include Sennheiser HD280, Equation Audio RP-21 or RP-22X, M-Audio Q40, Beyerdynamic DT770, audio-technica ATH-ES7 (or ATH-ESW9, but I think they're both supra-aural) and Denon AH-D1000 or AH-D1001. A slightly more unconventional choice, if you really have no budget, might be the Ultrasone Edition 9 (although the prospect of carrying them around and putting them at risk is terrifying
)
Bear in mind that I'm just a lowly n00b, if you will, and my opinions are formed only from what I've read here and on other sites. Unfortunately, headphone audio is quite hard to come by around here, so I personally haven't heard any of the headphones I'm considering. Erk...
By the way, if anyone's had the chance to compare the M50 and D1000 sonically, please post your thoughts.