Following the initial Quickstart docs you will find a lot of online documentation. The following are good places to start.
- The Interactive Shell
- Admin Zone
There is also a Getting Started however I found this a duplication of the Quickstart. I have not found an offline version of the manual, or a single HTML page version. This makes it a little difficult for reading without internet connectivity.
There are currently no books on MongoDB however there seems to be 4 books in the making.