The 2nd Edition of the MongoDB: The Definitive Guide from O'Reilly is one I can recommend (full disclosure: I was a technical reviewer on that edition). http://shop.oreilly.com/product/0636920028031.do
Finally, there are free MongoDB courses available at http://education.mongodb.com in various flavors of programming language, as well as an ops/DBA focused course.
For basics, the Little MongoDB Book (http://openmymind.net/2011/3/28/The-Little-MongoDB-Book/) is a bit dated at this stage, but a good starting point.
Finally, there are free MongoDB courses available at http://education.mongodb.com in various flavors of programming language, as well as an ops/DBA focused course.