Some monk (ikegami? kutsu?) recently pointed me towards plplot, which produces interesting plots. A (really) long-term project of mine would be to make OpenOffice.org really scriptable instead of relying on their ugly UNO stuff.

As OpenOffice.org documents are mostly (zipped) XML files, you could get away with one manual step by turning your diagram into a template and creating the output via Template Toolkit, then printing it/converting it to PDF from within OpenOffice.org.