Got one for the wife last year - a Cowon iAudio G3.
2 Gig, plays ogg (as well as all the other common formats).
No drivers required - can use it like a USB thumb drive to store even non-music files.
DOES NOT handle DRM.

Website says 50 hours on a single AA, that may be a stretch, though.

http://www.cowonamerica.com/products/iaudio/g3/

Doug