Great podcast - The Wild with Chris Morgan. Most recently about dogs trained to track bears, the secret lives of trees and Richard Louv. Great voice, great topics, great stories.

For more literary types, it's hard to beat the musings of Annie Dillard in Pilgrim at Tinker Creek.  

The Pursuit of Endurance by Jennifer Pharr Davis or any of her books really. 

Rowing to Lattitude, by Jill Fredstone.  She was (is?) an Alaskan avalanche expert who spent her summers rowing the coastlines of arctic places like Svalbard, Greenland, and the like.