My current set of headphones are a pair of Beyerdynamic DT-880 Pro.
I have been using this set of headphones every single day for around six months. So far the only thing to show any sign of wear are the pillow like velour ear cushions.
The more I use these headphones the more comfortable they become. When I first slipped them on they were a very tight. To solve this problem I left them on a one gallon water jug over night for a week. This loosened up the headphones enough to be comfortable and still fit well.
Overall the sound quality is superb. Which can be unfortunate at times since the majority of my incoming music is 128k mp3s. I quickly noticed how bad some of my favorite tracks sounded.
The output of these headphones is calibrated towards the low end. This is exactly what I was looking for in a set of headphones. They do not artificially amplify the low end frequencies, but rather highlight them in a pleasant way. If your looking for super bass thumpy headphones keep looking, these are not for you.
One very important note: not for the office. The open back design leaks sound so you will annoy your coworkers quickly.
I have not found an overwhelming reason to go out and buy an external amplifier for these cans yet. My MacBook pro powers them quite well. However I mostly listen to electronic music these days so YMMV. If I ever get the chance to borrow one I will certainly follow up on this note.
Headphones are a very important part of my life. I spend a lot of time thinking and coding in the flow of a long trance set. I am very happy with this set. They are comfortable, sound wonderful, and well designed. If these break for any reason what so ever, I would not hesitate to purchase them again.