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.
Noizio - Feeling that the noise of the big city is too much for you to bear?
Noizer - Ambient sounds like Noisli, but free
Defonic - Create a unique sound environment at home or in the office
Hear - Hear is a sound enhancement application for the Mac.
Studiowave - Chillout tunes and inspiration