Have you looked at Cowon? These are somewhat premium end players, but they are absolutely great. Their Cowon J3 was legendary, was declared the best mp3 player of all time by some outlets. I'm currently using a Cowon Plenue D2, which is also really good.
As someone that has worked with this for a year (pro edition): expose instances of this to the public at your own risk. This thing is riddled with security issues ranging from trivial to absolutely critical and the team developing this has completely ignored them, despite being repeatedly notified about them.
Also, if you start developing on top of this, expect the code and feature quality to rapidly drop once you get past the initial presentation.