Was in O2 today and picked up a couple of packs of the iPod socks for only £4.64. They were priced at £19 but when scanned through the till they went through at that price. They're the official iPod socks with 6 different colours in each pack and the exact same pack still retails for £19 at the apple store.
Will work with a wide variety of mobile phones/mp3 players including the iPhone as my lady is using one for her iPhone and it fits perfectly. I do realise you're paying mainly for the brand but at that price it makes a decent little add on present for Christmas.