Since no one's mentioned it yet, another alternative to Neo4J is AllegroGraph (though you need to pay for it; the free version supports 5 million tuples).
Please, not this thing about defense spending again ... you could feed and clothe them many times over, for many generations, with all the entitlement spending ...
It _does_ support bulk loading, with over 500K triples per second. According to http://franz.com/agraph/allegrograph/agraph_benchmarks.lhtml, given enough RAM, it can load over a billion tuples in just over half an hour.