Aside from the Shuffle, I haven't seen any iPods I'd want to take in the woods. It's a shame.
I like the Creative Zen Nano Plus. About 1oz and 1gig, flash-memory, 18hrs of play with a AAA, FM tuner. Pretty good sound quality and cool color options. The Plus models also come with an armband, I believe. I think it's one of the better values out there.
I've also been fascinated with the iRiver U10 for a while. 2.5oz, 1gig, flash-memory, 34hrs of audio, FM tuner. Pretty cool UI and also supports Ogg files, if that matters to you. Also might want to take a look at their T10 model, with a similar feature set and ~40hrs on a AA battery.
I'm not personally familiar with them, but Sony's mp3 products are reputed to be easy on the batteries.
If you can bear it, you can ring out more battery life by switching to lower bitrate riles, say mp3 files in the 96-112kbps range. You'll be able to get more from your batteries by avoiding audio files with DRM restrictions.