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.
zenmix.io - Ambient background sound generator
Noizio - Feeling that the noise of the big city is too much for you to bear?
Defonic - Create a unique sound environment at home or in the office
A Soft Murmur - Ambient sounds to wash away distraction.
Hear - Hear is a sound enhancement application for the Mac.