Apart from the guitar cord tuner and billable time tracker apps, I use my pda/phone/etc for all of the same things and a few others --- also on the Pocket PC platform. What specific plant and animal identification doc(s) do you use, and how do you like it/them? What format --- pdf, doc, or something else?

Ditto the star chart program --- that could be nice.

Just to potentially return the favor, I use a little freeware app that displays sun and moon rise & set times for one or multiple locations on my "today" screen, which I find handy when backpacking. If you're interested in that, have a look here:
http://www.freewareppc.com/astronomy/sunnmoon.shtml

Sorry for the blatant thread-drift; maybe a new "favorite pocket pc apps for backpacking" thread is warranted, dunno.