alternative product to IPOD and ZUNE?

I need to replace my IPOD. I am an Ubuntu user. Here are my desiderata: (1) Large storage (> 50GB) (2) I use almost exclusively mp3 files, so no need for iTunes (3) I need a good system for song navigation, as it currently exists on IPODs and ZUNEs. IPODs and ZUNEs are a pain to deal with, because you always need to synchronize with your computer (Windows at that!). Ideally, I'd just copy my mp3 files onto the device by file manager and be done with it, as is the case for a lot of che