The white-noise app Sleep Pillow Pro sends you off to slumber with an impressive choice of 70 sounds that you can play individually or combine into your own nocturnal symphony (300,000 combinations!). Traditional water- and nature-themed sounds are joined by oddities such as a galloping horse, a ticking stopwatch and, for the city girl, a speeding subway. You can program sounds to fade off after a specified amount of time, or use the alarm feature to have your noise gradually wake you up. Compatible with iOS for $1.99.
Note: Relax and Sleep is a similar free app for Android that has a fade-out feature and will also let you combine several of its 35 sounds. Frog swamp in a thunderstorm, anyone?