When writing program, we have an option to either write everything ourselves or to use/leverage on utilities/libraries that are already written. This is especially true when it comes to charting.
When using asp classic, you can use the mschart control that comes with MS Office. However, that requires that you install MS Office on your webserver. Also, I found the library quite difficult to work with.
The following are some popular opensource/freeware libraries you can use:
For Java, you can use jfreechart.
For .Net, you can use zedgraph. I saw a good article on this on this web page, which is in fact how I found this library.
Alternatively, you can use paid software, our previous software was chartfx and then we started working on Netchart.
Netchart is good in that it can be used for different platforms because it uses webservices and provides libraries for java, asp etc. Only thing it is requires a server to serve the webservices.
Some additional libraries that I found are:
Open Flash Chart
Fusion Chart Free A good sample code on how to use Fusion Chart Free using .net is found here.
Some additional java script charting components are found here.