Recently I've googled, digged around for good open source graph database. read some forum, stackoverflow. Then I've found OrientDB. Some people recommending it. It looks good. I think If ogm-orientdb module appear. I'll use it.

Some links:
https://github.com/orientechnologies/orientdb
http://orientdb.com/orientdb-vs-mongodb
http://orientdb.com/orientdb-vs-neo4j