This is a Japan-only product right now, but it was worth mentioning. The D-Snap SD800N is a noise-cancelling MP3 player that stores music on SD cards – did that ever work for people? – and is designed to work with Panasonic’s line of speakers and gear.
While I think noise-cancelling is great in theory, in practice it might suck. Imagine: you stuff this into your bag and it thinks the rustling of your papers is the sound of the ocean waves and tries to cancel it out. The audio might get kind of rough. I’d love to see it in action, though.