The Find Related Concepts API from IDOL OnDemand returns the most relevant terms and concepts from related documents. Here’s represented as a D3 Bubble Chart. Thanks to incredibly good work by Mike Bostock. For a description of the API go here https://www.idolondemand.com/developer/apis/findrelatedconcepts#overview
For D3 Data-Driven Documents go here: http://d3js.org