The Nokia 520 and 820 both have expandable storage, and Win8 mobile.
I listened to the 820 recently...and I liked it a lot. I honestly felt that the sound was more detailed and crisp than what I got from my 5g ipod touch. I felt like I could get more of the music's texture. Dolby headphone enhancement wasn't any good though. It would make portions of songs clip.
Unfortunately, no gapless :(
Which is very noticable, actually.
At the very least, these phones could give the Cowon's a run for the money.
And of course they can do a host of other things, like email, web surf, GPS navigation, and so on.
One annoyance I found is that the music management software is TERRIBLE. I transferred an album onto it and the album would be divided into two because the software somehow misread the information on the AAC files.