A fantastic background noise and color generator with a text editor for distraction free writing.
Noisli
myNoise
This site offers a unique collection of online noise generators shaped to your personal hearing thresholds allowing you to calibrate your listening experience.
Raining.fm
Cool Site - If you love listening to rain and thunder you'll love Raining.fm where you can create a custom mix of rain, rolling thunder, and cracking thunder to listen to.
Rainy Mood
Let the sound of rainfall with distant thunder soothe you when you need to relax or are having trouble falling asleep via Rainy Moods.