Web/iOS: We've talked about services that help you relax or become more productive with all sorts of soundscapes, from falling rain to cafe chatter. If the sound of birdsong helps you focus (it does for me), Birdsong.fm delivers.
Birdsong.fm is simple: an animated background and some singing birds in the background, sometimes accompanied by a few other nature sounds.
Click the menu button in the top right to see more options. From there you can grab the free iPhone and iPad app so you don't have to be tethered to your computer (additional sounds and landscapes are available in the app as in-app purchases), or you can click to buy a high-quality MP3 of the audio so you can listen to it wherever you like. Finally, if you fork over your email address, you get access to the "Nest," which gives you access to additional soundscapes, including a summer scene, a rainforest, and a few others, along with first access to new soundscapes as they're added. Hit the link below to give the service a spin.