So I was extolling the virtues of matplotlib previously, but I ran into a roadblock. I wanted to be able to generate imagemaps for some plots. So far I've been stumped in trying to recover the mapping from data coordinates to image coordinates.
Enter Advanced Software Engineering's ChartDirector, a commercial plotting library/component, with bindings for a bunch of languages. Even better ChartDirector will generate an HTML imagemap directly from a plot. Beyootiful, although I'd actually like the raw coordinates for other purposes. But it's easy to reverse engineer that.
Relatively straightforward and inexpensive licensing to boot.