Portapro
Koss Portapro headphones are easily powered by mp3 players. They are also cheaper than seins px100 200 series, though if you are more of a basshead you can choose the seins, cos thats what their famous for. If you rather have more accurately produced and balanced sound Portapro is what you need. Not only that, it is also able to compare with higher end headphones with only a fraction of the cost. Only $90 bucks, can get at Simlim or Causeway point. i have one such baby and if you read online, all the reviews are raving, as i am. They are really good, even though they were first manufactured way back in the 1970s!
Another choice if you want easier storage, or you dont want to look dumb in public, you can choose sony monitor EX series in ear eapieces for 80 bucks i think in simlim. Or if you got money to splash, get better quality in ears such as Shure e2c or (omg) e5c.