Sleep Cycle - Bio-alarm clock that wakes you up at optimal times based on your sleep patterns.
Pzizz - Sleep at the push of a button! Now with "Focus"
Sleep as Android - Common alarm clocks ignore your sleep cycles, they wake you on schedule no matter your are currently in your deep sleep. Waking up from deep sleep is unpleasant, it makes you tired and it may negatively affect your productivity during the whole day.
Rise: Track Sleep & Circadian - Wake up & fall asleep better
Sleep Calculator - Want to wake up in a good shape?
Enough Sleep - Boost your performance by getting enough sleep!