If you enjoyed Bruce Tate’s book Seven Languages in Seven Weeks you might also enjoy Seven Databases in Seven Weeks by Eric Redmond and Jim Wilson:

Data is getting bigger and more complex by the day, and so are your choices in handling it. From traditional RDBMS to newer NoSQL approaches, Seven Databases in Seven Weeks takes you on a tour of some of the hottest open source databases today.

Tate’s book also sparked a whole bunch of Github repositories with the code people write as they make their way though the book.