Sleep Cycle - Bio-alarm clock that wakes you up at optimal times based on your sleep patterns.

BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.

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.

Spotify - Map shows when two people play same song at same time

Talalarmo - Minimalistic android alarm

stats.fm - With the click of a button you'll be logged with your Spotify account and you'll instantly gain access to a valhalla of cool stats and insights.