If you're not opposed to running a Ruby utility, Genghis is a classic: http://genghisapp.com/
But for scalable production use, get yourself to MongoHQ.
Also, the Mongo Monitoring Service, from 10Gen, the makers of Mongo:
MongoClient is written in Meteor, Completely Free, Open Source And Cross-Platform.
RoboMongo Native cross-platform MongoDB management tool