Creative Labs 51FM5010AA003 TS Notebook 500 Speaker
Great for trips when you are bringing your laptop anyway
The great thing (or sucky thing depending on your perspective) is that these speakers are powered off your USB port.  If you are looking for something to listen to on the plane, the drain in battery life is most likely unacceptable.  But since you will be wedged in between a snoring 350 lb man and grandma Wilhelmina, you probably don't want to blast Girls Gone Wild 16 anyway.  They are also completely useless for your iPod for the same reason, which is probably why they failed in the marketplace.  If, however, you are going on a long trip where you generally have access to power for your laptop and want to listen to your music or movies with a full, rich sound, then these suckers are for you.  Set 'em next to the machine, clip 'em on top, or tuck 'em wherever you have space, plug them in, and kick back and relax.  They pump out plenty of power for anything other than a party (including a nice air guitar jam in your underwear in the hotel room) and sound really good.  The bass won't rattle the windows, but is really respectable for such a small package.  Finally, for those of us with our laptops sitting on the kitchen counter, the additional bonus is that they sound completely reasonable from behind as well so your mate won't complain that they can't hear the music while you work.