On top of using GD also check out DBD::Chart. I provides a DBI interface to charting, you can insert your data into "tables" and then generate charts and graphs off of it. Or you can pull the data out of your existing tables and chart it.
It supports a wide variety of highly configurable chart and graphs. It also will generate imagmaps for client side mouseovers and navigation.
All in all, a great package. The kind of package that you can use to blow your boss or client away with.

-pete
Entropy is not what is used to be.