Currys/PC World shops, demo the Sennheiser range.
I had a look into one of the new Currys and PC World mega store yesterday. They have a headphone demo area with most of the Sennheiser range from £25 to £150. You can listen to a selection of their own music or take along your own mp3 player and plug it in. I think it was 16 headphones in all. Very impressive, if you want to demo Sennheisers.
Then there was the entire Monster Beats Dr Dre range and at the ipod stand various Philips headphones.