Today, as I am leaving for holidays tomorrow, I bought a new MP3 player. As buying hardware that works with Linux is like lottery, I just picked the one I liked best without even considering how it might work with Linux.
But today, I've won the Linux-Lottery. The MP3 player is fully usable by just mounting it and transferring your music to the music folder. All that even though the package explicitly stated that the product does only work with Windows. I already transferred a lot of music onto it so I can listed to it while sitting in the train. I am pretty satisfied with it, the only shortcoming is that it is only chargeable by USB, but that is not that bad as I am taking a laptop there anyway.
The only thing that, I think, is impossible with Linux is making playlists, but as I never use that feature on mobile MP3 devices anyway, it is not that bad.
It was a Sony NWZ-A826, if you are interested in buying an MP3 player that is well-supported under Linux.