Thanks! It's surprising how we still don't have a good open source charting library. I've checked most of them out and Highcharts/FusionCharts blow them out of the water.
I think we have far too many good open source charting libraries, it makes picking very difficult.
There are a number of great open source charting libraries that don't force you into really inflexible APIs or require you to transform data into a hard-to-use format to display it. NVD3 is (for me) much easier to use and customize (not to mention looks better and can be customized with CSS) than HighCharts, for example. The latest FusionCharts offering looks more straightforward but their pricing model is a no-go for me.