http://sparkline.org/
It is worth digging through the excellent collection here (Flash, JS, PHP, etc.):
http://www.webappers.com/category/components/charts/
Being a mootooler I always prefer Mootools Javascript charts:
- http://blog.greghoustondesign.com/canvas-pie-chart-with-tooltips/
- http://highcharts.com/
- http://moochart.coneri.se/
- http://www.copix.org/index.php/wiki/Mootools/Charts/en
