I have tried about five different graphing suites, but the nicest results have been from Open Flash Charts, which is what I'm currently using.
I don't know if you've tried it but I rather like the
flot library. I used it on my
Fresnel page, for example. It involves some JavaScript programming in the web page which might be seen as a minus but does have the advantage of simplifying things dramatically on the server making very low power servers practical.