I have decided that as well as getting a decent amp and speakers I should treat myself to a new pair of headphones, to replace the iPod headphones. The set that comes with the iPod is fine for a quiet room, but on a street or even a train you loose so much of the detail. I hunted around a bit and was very tempted by the Grado SR-60s, which seem the best sub 100 pound headphones to all accounts, but I want something I can carry to and from work. What Hifi had the answer in the form of the Sennheiser PX100 (amazon uk), which I paid over the odds for, from Virgin, as I wanted them there and then. They should be about 20-30 quid, depending on who you buy from, amazon uk have them for 22.49, they are cheaper again on amazon us.
So what are they like, well they are very comfortable, as they sit on the surface of the ear and do not try to deform the pinna. This is in part due to their design and an also due to their weight of only 60g. They come with a clever folding case to store them inside and they fold themselves in to thirds, with the earpads / speakers twisting and locking flat, there is also storage for the cable, see the pictures on the sennheiser site above, or this how to fold PDF.
In terms of audio they are pretty amazing for 30 odd quid, clear detailed sound with a real sense of separation between say the bass drum and the guitars. I have noticed lots of detail in recording I thought I knew well. They are also loud enough to make your ears ring after listening to the White Stripes at full volume from an iPod and they cope very well with LFO. Probably the best upgrade you can buy for your iPod.
I used to have a pair of wonderful Sennheiser HD 320s, which were one of the best headphones of the early 90s, after nearly a decade of hard work they finally became too broken to fix. So I went and impulse bought a big shiny set of Sony cans, which I never really liked, as they were a closed back set. Hence my raving for the new Senheiser PX100s, which are also open backed. This means I'll get the odd annoyed look on the train, but at least the music will sound great.