When buying in-ear headphones, you need to account for sound and build quality, but fit is also of utmost importance. When you find a pair of in-ear headphones that are liked by many different people—with very different ears—you’ve found something special.
A good pair of in-ear headphones should sound even across the entire frequency range. In other words, the bass guitar shouldn’t overpower the lead guitar, the lead guitar shouldn’t make you lose detail in the vocals, and the vocals shouldn’t have consonants that are painfully, piercingly loud. The headphones should have crisp, clear details (without being harsh), and a low end that has pitch and form to it (not just be whump whump whump)… More at engadget.
I tend to find that headphones are very much a personal thing, but this is a decent round-up which may help you decide what to get next.