I really enjoy "The Meateater Podcast", hosted by Steven Rinella. Great information about hunting, conservation, and public land, with guests including hunters, biology researchers, Joe Rogan, state Fish & Game employees, and authors. Even if you're not a hunter, the discussions are fascinating.

There's a few ads in the earliest episodes, but otherwise they keep it to the occasional "Hey ya freeloaders, go rate us on iTunes" at the start of the show.