Brain.fm - Music designed for the brain to enhance focus, relaxation, meditation, naps and sleep within 10 - 15 minutes of use.
Moszen - Moszen is a free web service that provides ambient sounds from natural environments to help you relax and avoid stress in your daily life.
MyNoise - Custom shaped online noise machines. Many Many generic sounds
Noises Online - Premium masking sounds
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.
SoliCall Pro - Removes noise & echo from any VoIP call. Can also be used for call recording.