I have some specific requirements, with the most important at the top:
Can plot line and stacked bar charts
Can customize mouse events (hover, click) on chart data
Compatible and performant with IE7/8 (likely will use excanvas.js)
Can optionally control label formats, legends, colors
Open source preferred, or at least can purchase the source
Can be hosted locally
I have seen a couple potentially good ones:
Google's interactive charts (But code must be accessed via Google servers)
EJSChart
Flot
Does anyone have experience with these, or others, and can make a recommendation?