To use this app simple have your ModelAdmin subclass django_histograms.admin.HistogramAdmin and give it a histogram_field attribute with the name of a DateField or DateTimeField to create the histogram over. Then you can pull up localhost:8000/your_app/your_model/report/ to see the histogram (adjust the URL as necessary).
The designs came from Wilson Miner's article on data visualization for A List Apart.
You can use the built-in histogram_for template tag:
{% load histograms %}
{% histogram_for 'appname.Model' 'histogram_field' %}