We have been extremely impressed with GoJS. As a library, it's logical, well thought-out, expansive, and written in a way that allows almost unlimited opportunities. When we took it on, we didn't know how much eye candy it could support without performance strain, but these guys know their stuff and our users love to use it. Support, too, when we have needed it, has been first rate. I wouldn't hesitate to recommend GoJS to anyone looking to do graph visualization and interaction in a browser. It's helped make our risk management and visualization application, RiskView, world-class.
Meercat Pty Ltd