As a Scrum Master I have some favorites metrics which I usually use it.
*Burndown chart - used daily as an indicator how the sprint is going.
*Velocity and velocity variation - i use a three to six sprint rolling average.
*Sprint goal success rates.
*Time Blocked per User story.
*Average time between releases.
*Build time. This metrics are intented to be used by the team to help us to improve our processes and are not intended to be use for any reporting outside the team. Some articles that I found interesting related with metrics: