Ive been recently looking for a headphones too.
What I've found out is - headphones as a main monitoring gear instead of real studio monitors is not a good idea ( you probably knew that - I didnt
)It's mainly because of the different dynamics impression on headphones ( another thing - closedback cans~better dynamics, openback cans - worse )
Aside from this dynamics thing, it's just hard for the headphones to sound just flat. They almost always colour the sound in a way. ( check those 300usd cans - it's really flat frequency response in comparison to the cheaper ones, but still, not the one we could dream of.)
When choosing headphones, read as many reviews as you can. Some headphones - especially those with closedback cans - can be tiring in the long run. There is no airflow between the closed space of the headphone and the outside ( unlike in openback/halfopen headphones ). Comfort is really important. No review though will replace checking them out in store by yourself.
The other thing is the price. Yeah, I wanted to pay like 400$ for headphones ( those beyerdynamics ) just to know that I bought the quality. But then I read that I'd need additional amplifier ( another ~200$ ) to really use their potential... fuckouttahere...
There is of course an option to buy them ^used, but as with everything used, its a lottery. To me headphones are like socks - I aint buying them used - sorry
Plus, 5 times more expensive headphones arent even 3 times better. Shit, they cant be... Plus, what kind of a professional sound I want to create with them? Shit, I dont care about the proffessional sound, I like it lo-fi and shitty-quality, just dope melodies.
soooo, to sum up and give you some nice recommendations - from what I read on few forums yesterday:
<100 usd - ( im getting those even though their looks just wack ) Sennheiser HD 438 http://www.headphone.com/headphones/sen ... hd-438.php
+ closedback cans, pretty comfortable, price, acceptable frequency response, no amplifier needed
- looks, higher frequencies
<300 usd ( I wanted them sooo bad because of their comfort plus openback thing ) Audio Technica ATH-AD700 http://www.headphone.com/headphones/aud ... -ad700.php
also these Audio-Technica ATH-M50 ( big bang for a buck, good opinions, not the best for longer listening sessions, closedback ) http://www.headphone.com/headphones/aud ... th-m50.php
>300 usd ( my first choise but like I wrote, I changed my mind )top notch, hand made quality, ultra-comfortable, really nice frequency response ) Beyerdynamic DT 880 + some decent headphone amplifier
http://www.headphone.com/headphones/bey ... dt-880.php