Flot is a jQuery plugin for easily creating good-looking and interactive charts. The library uses HTML5 canvas for drawing, JSON as the data source and can render a data array with 1000s of items.
It is not limited to any chart type and the community has already expanded it with multiple types (bar, line, pie, gantt, etc.) and features.
There is support for zooming into any selected part and charts generated can respond to events. Flot is very well-documented, has a powerful API and an active community