On his blog, Andreas Gohr has posted about various charting applications on the web (in his search for a way to show off the stats for DokuWiki) and looking specifically at the Google Charts.

Because such [popularity] data is much better to comprehend when accompanied by some nice graphs, I had a look at the Google Chart API today.

He also mentions three wrapper libraries that help your apps interface with the Charts API. Of course, he also includes some graphs of the popularity stats showing things like web server usage and PHP versions.