You've probably heard Lang Elliot's work even if you have no idea who he is. He is widely considered the major force in recording birdsong and is the primary bird song recordist for the Eastern Stokes Guide. He and some friends have put together a blog of nature music - birds and frogs and other fauna. It's the perfect antidote to a gloomy depressing day.
I stole this video from his blog. You should check it out here: The Music Of Nature.