Google Chart Tools
The library is compatible with all major browser and also run on iPhone and iPod. Thee library support tooltips, text Rotation for Labels, zooming and inverted Chart or Reversed Axis. Through a full API you can add, remove and modify series and points or modify axes at any time after chart creation. Higcharts library is free for non-commercial.
Canvas element to plot graph in modern web browsers. It has a rich API to draw different kinds of graphs such as line, bar, pie, gantt.
PieCon: Progress Pie Charts in Favicon
Piecon allows to generate pie charts progress pie charts in your favicons dynamically. You can set the color and shadow of pie charts in favicons. Piecon is supported in Modern browsers such as IE9+, Chrome 15+, Opera 11+.