I tried DB Visualizer (on RH8) some time ago and it has a very slick UI but I was was unable to print any significant portion of the datamodel in a form that was readable. You may have better luck.
Then I tried DataArchitect (from thekompany) which did print but does not look as good initially. If you ask it to show the entire 'core' datamodel it doesn't arrange the tables very neatly so you have to spend some moving tables around and grouping them.
