Jason Kottke pointed out that BBC Unplugged has released four fantastic videos that run to 10 hours each. They contain footage shot for the BBC’s Earth 2 series along with a range of ambient nature sounds.
If you are looking for something relaxing you can run on your TV while you work or do things around the house (or office), you will probably love this. My favourite, so far, is the Mountain Sounds video:
Here is the YouTube playlist with the whole set:
Image credit: Scott Webb