Graphs make boring numbers look pretty - there's no denying it. Graphs though tend to be hard to create dynamically. There are two different frameworks you can use though to make life easier. The first of these is "Flot", a plugin to be used with jQuery. Flot uses the canvas tag to draw one of several graph types on the page. It also has the ability to draw multiple graphs on the same graph. However it isn't something that would be easy for your users to right-click on and save. If you need that ability then you will need to try the Google Chart API.
Flot is a pure Javascript plotting library for jQuery. It produces graphical plots of arbitrary datasets on-the-fly client-side.
The focus is on simple usage (all settings are optional), attractive looks and interactive features like zooming.
Link: Flot for jQuery
The second of these is developed by the behemoth that is Google. The Google Chart API can generate several types of graphs and returns the result as a PNG image. It's probably harder to use due to it passing multiple parameters to a URL; though if you've got a references to which parameter does what it shouldn't be a problem. This one can also do all that Flot can, plus a little more.
Link: Google Chart API
