jFreeChart would have to be one of our favourite Java charting libraries. With a powerful system that is included with a lot of other projects, for example JBoss, etc...
This, coupled with a vibrant development ad support community behind it, you just simply cannot go wrong.
We have used jFreeChart for many projects and is our default charting library.
Unfortunately, some people do seem to have some problems with the library, so we will go through a simple tutorial that aims to give the foundations of the charting library.