dc.js is one of those libraries that completely blows client's minds. The hard thing to do as a developer is not to try and filter the data too much. dc.js lets the end-user filter the data interactively and create their own stories, you just have to work out the questions each chart lets the user ask. http://dc-js.github.io/dc.js/

As it sits on top of crossfilter (http://square.github.io/crossfilter/) you can also do unusual things behind the scenes to the data sets. As an example, I used google maps to restrict datasets to the current map view. Worked surprisingly well. http://www.bathhacked.org/projects/hacked21-food-standards/

I really enjoyed using dc.js. It also rolls in crossfilter which is awesome for drilling down into data.