I have Sony Funtopia earphones, I highly recommend them, they come with 3 different sized rubber earbuds to fit anyones ears, with the earphones in and no music playing sounds like you're underwater, you can hear your breathing quite loudly but nothing else really. Turn on the music and you'll be supprised at what you hear, it really takes advantage of the iPod and music with high bit-rates, I often notice things in my music that I'm usually unaware of and the bass is excellent.
I use them everywhere, even through Lakeside Shopping Centre in the middle of the christmas shopping period and I still hear nothing but my music.
They're about $50 (£25) but worth getting to make the most of your iPod.