I've released MdeGraph. It's a javascript library for creating canvas based graphs. Below is an example, with the same data as the (static) graph in this article.
As a demonstration of how these values are calculated client-side and realtime, you can adjust the value for the red line above the 1999 marker by choosing a value here:
Update 28-11-2011: there seems to be an error in version 1.2 with calculating the position of the mouse, causing the labels to fail. Nevertheless, the example.html on my bitbucket page works fine. I'll see if I can fix that soon.
Update 18-12-2011: fixed the positioning error in version 1.3, so enjoy labels upon hovering over the bullets!