Blanket - Improve focus and increase your productivity by listening to different sounds. Or allows you to fall asleep in a noisy environment.
Sounds of Earth - Listen to relaxing ambient sounds of nature
MyNoise - Custom shaped online noise machines. Many Many generic sounds
Noizer - Ambient sounds like Noisli, but free
Noisli - Noisli is a fantastic background noise and color generator for working and relaxing. Online soothing ambient sounds like White noise, Rain and Coffee Shop.
Ambie - Beautiful white noise app to help focus, sleep, or meditate.