Brain.fm - Music designed for the brain to enhance focus, relaxation, meditation, naps and sleep within 10 - 15 minutes of use.
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.
MyNoise - Custom shaped online noise machines. Many Many generic sounds
Noizio - Feeling that the noise of the big city is too much for you to bear?
A Soft Murmur - Ambient sounds to wash away distraction.
Blanket - Improve focus and increase your productivity by listening to different sounds. Or allows you to fall asleep in a noisy environment.