[Updating post to add more libs.]
Okay. I got called out for not poking around a bit more. There are nice open-source, liberally licensed JS chart libs.
gRaphael : built on the awesome Raphael JS vector graphics library. Limited functionality, but that’ll change.
Canvas3D : super cool, but not sure if it’s ready for a production site…
jqPlot : charting for jQuery. I’m neither pro- nor con-jQuery, so I’m not sure that I’d pick a jQuery-centric library.
PlotKit : dependent on MochiKit.
Flot : charting for jQuery. Again, since I use different JS libraries in different circumstances/apps, I’m not excited about having to pull in jQuery, but Flot looks nice.
Emprise Charts : Very nice. Pricing is inline with JSCharts and HighCharts.