I have posted reviews of a few different earphone or earbud options on this travel gear blog. For most travelers, earbuds are the best option because they pack up so small and the right ones can passively block out a lot of noise over a wide frequency range. Some people are a lot more comfortable with regular headphones though, so these Sennheiser PXC 300 noise-cancellation ones manage to kick out a fantastic sonic experience but are not as bulky as the more popular Bose models.
These are good for travelers like the person who commented on my Koss earphones review -- people who find that earbuds get uncomfortable after a while. (I'd say though if you can wear squishy earplugs to bed and they don't bother you, you might have better luck with the Comply Noise Reducing Earplugs.)
The Sennheiser PXC300 headphones are wonders of technology, so they'll probably cost you at least $150. These use active noise cancellation, which means when you hit the button to turn on the battery pack, you not only pump up the volume but a lot of the extraneous noise around you gets cancelled out. Long explanation short, there's a little mic on the outside that picks up the noise around you and emits the opposite sound wave in your ear to neutralize it. Thus the "noise cancellation." It works best on long continuous hums though: airplane engine roars and the hiss of cabin ventilation systems---not that crying baby in the seat behind you.
Considering what they deliver, these are super-light and they only require two AAA batteries. They crank out incredible sound whether you've got the very best iPod or the very cheapest MP3 player. A little jamming and cord wrapping is required to get both the headphones and the battery pack into the too-simple soft carrying case, but once that's done it's a little larger than a portable hard drive or a bit smaller than a mass-market paperback. Also included are adapters for a regular stereo jack and the two-pronged audio outlets on many airplanes. Plus they come with a 2-year warranty.
The technical specs on these Sennheiser headphones are comparable to rival models costing far more and unlike models from some competitors, these will still work passively when the batteries run out of power. You just won't get the incredible bass response you do with the juice flowing. If you spend a lot of time shuttling around on airplanes and are willing to make a little extra room in your bag, these headphones will deliver a great listening experience and help shut out some of the ambient noise around you.
Get the Sennheiser PXC 300 headphones from Amazon