I voted "go for something cheaper". Grado has iPod headphones for $49, that some people claim sounds better than most any iPod cans, including the Sennheisers and others that cost over 100 dollars.
Grado - I-Grado iPod/MP3 Headphones-Audio Advisor
Amazon also has them listed.

I don't have the Grado iPod headphones, but I do own a full size professional Grado headphone, and their headphone amp. The Grado phones aren't the most comfortable to wear, but their sound is first-rate. If I ever need new phones for use with portable playback equipment, I wouldn't hesitate to get Grado's smallest model.