A Mysql MWB File that can be modified. moodle_33_erd.mwb .This file contains additional diagrams that show some of the modules in more detail.
A pdf rendering moodle_33_erd.pdf. A set of images of individual components of the diagram components

How the diagram was created, Diagram FAQ. See here for an archive of  old versions. There is a file containing the xml that creates all tables here and files matching the plugin here