As a PC gamer and music listener, I recently bought an Asus Xonar D2X, which was my first ever dedicated sound card (I'm a little ashamed to say on these forums :P), and the quality compared to integrated blew me away.
Now though, I want a decent set of headphones to go with them. They won't be moved around at all, I just need them to be as comfortable as possible as I will have them on probably ~8 hours a day, with work and play, and have the best sound quality possible, around £50-60, but may be able to stretch a little more depending on money closer to the time.
Finally, where is a good place to buy audio gear in the UK? I know places like Amazon and Play will probably sell them, but as someone that builds computers, I know that shops dedicated to selling hardware are better than your "jack of all trade" e-tailers like Amazon, so I assume this will also be the case with audio hardware, that the shops will have a much wider selection and probably much better prices and support too.