dc.js v0.8 released with choropleth chart support, checkout the new US Venture Capital Landscape example to see how it works in action.
v0.8 release has also introduced new ability to encode data in coloring for bubble/pie/choropleth charts. See updated Nasdaq 100 example:
On top of that v0.8 release has introduced a truck load of bug fixes and enhancement including some significant performance improvement (see release notes). Try it out and have fun visualizing =)