Here are a few D3 demonstrations from class that you may find useful:

Streaming Twitter Data
This visualization subscribes to a live feed to twitter data and watches for occurrences of pre-defined keywords in the tweets. The visualization shows tweets that contain these keywords, as well as a bar graph that shows the percent of all tweets that contain each keyword.
Gender Distribution in the US
This visualization uses US Census Data from to show the proportion of female residents in each county of the United States. The fill color of each county is scaled to clearly show whether the county is majority female, evenly split, or majority male.