SnapDir
This a site where you can store and view your d3.js visualizations. Up until now you can only use about 3 d3.js templates, maybe more in the future. The ones available now are useful to view directory listings (therefore the name, beware of their size though, only a certain number of nodes will 'fit' into your browser) There are also ways to interact with other members of the site and get shared content.
The json file you supply has to be a valid json file that is structured over parent/children relationships.