If you need help with MongoDB, following are the sites and resources you should find invaluable.
Homepage: http://www.mongodb.org/
Official MongoDB documentation: http://docs.mongodb.org/manual/
Official issues and features tracker: https://jira.mongodb.org/
Official mailing list: http://groups.google.com/group/mongodb-announce
The MongoDB operator reference page is something to be bookmarked as it would be widely used in many scenarios: http://docs.mongodb.org/manual/reference/operator/
10Gen is the company behind MongoDB and offers commercial support too. The company's URL: http://www.10gen.com/
A collection of white papers can be found here: http://www.10gen.com/datasheets-and-white-papers
An exceptionally large archive of presentations on MongoDB will be found at: http://www.10gen.com/presentations
Every now and then 10 Gen conducts some free online courses on Mongo. You may watch out for them at: https://education.10gen.com/
Get an overview of some of the Mongo's production deployments here: http://www.mongodb.org/about/production-deployments/
A couple of interactive MongoDB tutorials can be found here: http://mongly.openmymind.net/tutorial/index and http://try.mongodb.org/
Official MongoDB blog: http://blog.mongodb.org/
Stackoverflow forum and questions on MongoDB can be found here: http://stackoverflow.com/questions/tagged/mongodb
