The Scrum Field Guide, Mitch Lacey.
Although it’s subtitled “Practical Advice for Your First Year,” Mitch Lacey has loaded his book with so much good advice that even veteran Scrum Masters will find themselves reaching for it from time to time, especially when creating new teams or joining a new organization.
Succeeding with Agile, Mike Cohn.
Another excellent resource for Scrum Masters introducing Scrum to a new organization, including lots of advice on how to start from scratch in companies that have never been Agile.
Scrum: The Art of Doing Twice the Work in Half the Time, Jeff Sutherland
Jeff Sutherland helped create Scrum, and his recent book explains not just what Scrum is and how it works, but how and why it was designed the way it was. Any Scrum Master who has been stumped by questions about why a Scrum ceremony or artifact is important will find the answer here.
Sam Falco 