MongoDB offers test data in its official tutorial "Aggregation with the Zip Code Data Set" at http://docs.mongodb.org/v2.4/tutorial/aggregation-zip-code-data-set/. I modified it to make it possible to test embedded documents.
The original test data may be downloaded from http://media.mongodb.org/zips.json.
The new test data "zips-embedded-documents.json" was got by running the PHP script "t.php" from the command line.