Maybe graphdb people won't like this, but I'd like to try their very nice browser with a couple of existing SPARQL endpoints, based on Virtuoso, Fuseki, who-knows-what (in the sense that they're not under my control, e.g. DBPedia).
I wonder if their product is available standalone, outside of their DB (which is really good anyway), to support this use case.
Alternatively, is there a similar browser around (I'm mainly interested in graphical representations, which are so Neo4j-like).
GraphDB (RDF database) offers a highly customisable and generic interface similar to neo4j. With Visual graphs, you can configure how the RDF graph is mapped to the visualization graph. Often the RDF graph is too fine-grained to be directly presented because it's designed to represent a generic domain with all its specifics as an ontology. A very common task rendering RDF data is to map a relation class (in RDF all N-ary relationships are modelled as a concept) as a direct link (predicate). Thus, any RDF data model can output multiple application-specific graphs.
You can use SPARQL 1.1 federation to query remote instances. When the query does not perform a remote join its execution time should be acceptable. To see a live demonstration over a very large repository check the FactForge's public service demo.
Disclaimer: I'm associated with the GraphDB product development.