in last 10 minutes
Graphing and drawing with OpenACS
Competitive analysis of graphing solutions on Aolserver/OpenACS
Graphviz seems to be good for many types of diagrams. Webdot is a Tcl based cgi app for producing images from .dot files. However, it seems like it's best for network diagram type diagrams.
SVG seems like the best option, although there is no current browser support for it. Adobe browser plugins for SVG are available, however. SVG Printing is also only in the specification stage now, so printing is problematic still. SVG is the way to go overall, though.
Reportlab generates PDF documents. They can be generated dynamically, and this is probably the solution with the highest degree of control. However, the API takes a while to get used to.
Chartdir, a non-free but very nice charting program.
nschartdir, using ChartDirector (http://www.crystalballinc.com/vlad/software)
jpgraph - http://www.jpgraph.org
Eclipse (http://www.eclipse.org). Its often thought of as Java-centric, but its supposed to be language-neutral, and they have several projects to enable it to support other languages (http://www.eclipse.org/tools/index.html) using its plug-in architecture. They also just came out with a UML toolkit that you might be able to leverage (http://www.eclipse.org/uml2/)
Fusion Charts - http://www.infosoftglobal.com/FusionCharts/. Its not open-source or even free
but at only $99 for an unlimited license its very reasonable. The results are very good.
GForge - http://www.gforge.org