As developers we're always appreciative of documentation that lets us absorb a lot of detailed information as quickly as possible. While nothing can replace a detailed reading of the core MongoDB documentation from 10gen, a few pages of pithy reminders can make operational life a lot easier.
MongoLab sponsored the recent DZone reference card for MongoDB. Here's a little snippet below. Download the rest of it here http://refcardz.dzone.com/refcardz/mongodb. (registration with DZone required)
Thanks to Kristina Chodorow and the 10gen crew for a nice reference card and to the folks at DZone for producing it!
UPDATE 2013-02-06: added note saying that DZone requires registration