If you have $300 to spare, the Bose Quiet Comfort 2 headset is easily the most comfortable set of headphones I've ever owned. The biggest drawbacks to them are the fact that they are a regular over-the-ear full sized headphone and the fact that they use a AAA battery to power them. They are a noise canceling headset so need the battery to operate, but they also suppress outside noise pretty darn well (so you can't hear Mom and Dad yelling for you to take out the garbage ).
I would highly recommend the Sennheiser HD280 series or some other set that shares the same design as they do not apply pressure to your ears, but create a cup around them. This is IMO the best design for long use as even the most comfortable headphones begin to itch or burn after an hour or so.
Comments
http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=A331064&ts=04622&id=15532
There's some cool stuff on that site, do they have a US sister site?