MP3 player

[Theosus]

I just use the phone. If the screen is off and it's just playing music, the battery lasts forever. Couple that with a 5Ah charger and you could go for days on the trail and not worry about the battery. I used to have a sansa AAA battery-powered mp3 player, but its main problem was the volume knob. Instead of being digital like most virtual on screen controls, it was an old-school wheel, the first thing to fail on most radios and such. The contacts get dirty, stuff breaks, and soon your volume knob operates scratchy or not at all, and you lose one side or the other on your headphones. I record my music off xm or just use "YouTube Downloader", so we aren't talking having to have perfect quality reproductions... But the phone does a pretty good job.

[eblanche]

If you will carry a big enough external battery, I'd say maybe just use your phone for everything. Otherwise, I also recommend the Sansa Clip line of mp3 players. I used the sport and it barely lasted the through hike. I'm sure moisture has played a part. They are cheap and have a lot of features but I will say that there are also many complaints about them failing prematurely.

For headphones/earphones, I would use open ear or just not something in-the-ear that will block out all noise. Just a personal preference. Just make sure they are comfortable and stay in your ears when bouncing around if you plan on hiking with them. I find the stock iphone buds annoying as the volume toggle weighs one earphone down causing it to come out but cheap and decent enough.