I\'ve heard about MongoDB, but I\'m not sure I fully understand the concept.
If I have multiple JSON objects stored in MongoDB:
[{\"id\": \"peter\",
\
MongoDB stores data in BSON format which is similar to JSON. You can store data in JSON format and can make a query on any field. You can even index on a particular field which is used for major queries.
You are not limited to MongoDB, Seeing your question i think any of the Document-store will suit your needs. You read more here :- http://en.wikipedia.org/wiki/Document-oriented_database