MongoDB ETL (php/java...)
Pentaho Data Integration supports MongoDB (See the documentation http://wiki.pentaho.com/display/EAI/Pentaho+Data+Integration+Steps).
Similarly Talend supports MongoDB: https://github.com/adrien-mogenet/tMongoDBConnection
For simple inserts of CSV documents I would suggest looking at the Mongo wiki page Import Export Tools.
For anything more complicated I'd suggest writing an ad-hoc script in the language you are most comfortable with.
It seems that Pentaho Data Integration and Talend only supports reading from MongoDB, but not writing.
Another tool that just announced support for MongoDB is DataCleaner, and it supports both read and write operations. It does not position itself quite as an ETL tool, but more like a data quality analysis tool, but it does have ETL-like capabilities also.