Just published dc.js v0.5 release with support for composite chart.
Currently dc.js allows you to compose multiple bar chart and line chart into a single composite chart as shown in the above screen capture. Some minor API changes have also been introduced in this release to improve readability.
xValue() => keyRetriever()
yValue() => valueRetriever()
rValue() => radiusValueRetriever()
Check it out and enjoy http://nickqizhu.github.com/dc.js/