Official documentation for Flex charting
Source included with this useful Flex charting example
A gallery of examples of Flex charting features
The industry standard data logging and graphing application. Use it to write your custom monitoring shell scripts or create whole applications using its Perl, Python or PHP bindings.
Cacti is a complete network graphing solution designed to harness the power of RRDTool's data storage and graphing functionality. Cacti provides a fast poller, advanced graph templating, multiple data acquisition methods, and user management features out
JFree.org is home to a number of free software projects targetting the Java platform. Includes JFreeChart.