Google Chart API lets you embed small charts by calling a URL to Google’s service. Here is a Hello World example URL and the chart.

http://chart.apis.google.com/chart?cht=p3&chd=s:hW&chs=
250x100&chl=Hello|World

You get 50,000 charts a day free. With some local caching that can go a long way. I suppose later you will be able to rent the service.