Sleep Cycle app as an alarm clock. Graphs how you deeply you slept, depending how much you moved during the night.
It claims to wake you up during the lightest sleep stage so you feel well rested. In the nearly 3 months I've used it, this happened 5 times. Still, interesting app. Worth the 99¢ to get a better picture of your sleeping habits.
Related: The sleepyti.me bedtime calculator