Rainy Mood - Rainy Mood is the world's most popular rain simulator. Sleep, study, and relax with the sound of rain.
Blanket - Improve focus and increase your productivity by listening to different sounds. Or allows you to fall asleep in a noisy environment.
Calm - Calm.com can help you reduce stress and increase calm.
MyNoise - Custom shaped online noise machines. Many Many generic sounds
A Soft Murmur - Ambient sounds to wash away distraction.
Brain.fm - Music designed for the brain to enhance focus, relaxation, meditation, naps and sleep within 10 - 15 minutes of use.