Chart API

jQuery Charts:
gRaphael — JavaScript plotting Library
http://g.raphaeljs.com/

Flot - Attractive Javascript plotting for jQuery
http://www.flotcharts.org/
http://drupal.org/project/flot
Flot - How to Add Charts to your Web Pages:
http://www.pikemere.co.uk/blog/flot-how-to-create-charts/
Flot - How to create line charts:
http://www.pikemere.co.uk/blog/flot-how-to-create-line-graphs/


Google Charts:
https://code.google.com/apis/ajax/playground/?type=visualization

Microsoft Chart:
Microsoft Chart Controls for Microsoft .NET Framework 3.5:
http://www.microsoft.com/en-hk/download/details.aspx?id=14422

Microsoft Chart Controls Add-on for Microsoft Visual Studio 2008 (VS Studio ToolBox > Data > Chart)
http://www.microsoft.com/en-us/download/details.aspx?id=23903

Microsoft Chart Controls for .NET Framework Documentation
http://www.microsoft.com/en-us/download/details.aspx?id=11001

Video: how to use Microsoft's Chart Control in your Application
http://www.youtube.com/watch?v=bRnUAwUFIgY