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.
Best MongoDB training I had was to be at a company where they throw it into production, it crashed almost every day and then we got 10Gen to train us on what was going on. I got experience and wisdom all in a very short time.