myNoise has great nature sounds
In the mean time, someone showed me mynoise.net from a guy who has been traveling the world for years searching for and recording nature sounds.
His website has built-in controls so you can create your own mixes. It’s actually quite similar to the concepts used in Guided Meditation Treks, with the volume faders. In this case, your nature sound mix is created from a bunch of different elements, which are essentially just different microphone placements. It’s a really awesome site, here’s rain on a tent to get you started.