Coby MP305-4G: cheap, flash-based 4GB storage w/ FM radio. Uses one AAA battery. Supposedly supports drag-n-drop feeding, and purportedly a folder file structure as well. Drawback is that quality control is questionable at best, and product life longevity is definitely NOT a given. Fact is, you're probably going to replace the Coby LONG before any Li-ion battery in another device would give up the ghost.

The easy, user-replaceable battery criteria is a hard one to get around these days...unless you buy an unlocked cell phone (non-iPhone, that is) that can play digital music and other content...and use it ONLY for playing that content. At least with most cellphones removable batteries are generally the rule rather than the exception. That said, most PMP and DAPs these days can have their hardwired, rechargeable batteries replaced...naturally, for a fee. But considering what off-the-shelf, disposable batteries cost over time, it could easily be a wash as to which method is really more expensive. And if you're brave enough, you can even do it yourself rather than have a service replace it. I've done it with a couple or so iPods over the years, and besides seeming a bit daunting ("oh, I'm just going to mess it up..."), it really wasn't all that difficult to do, especially with Google and the internet to help guide the do-it-yourselfer.