I just popped over to http://www.fabforce.net/dbdesigner4/ to see their latest DBDesigner4 modeling tool and its quite lovely.
For example you connect to your mysql database of choice choose DATABASE->Reverse Engineer and you get a UML mockup of your database.
check out a screenshot here http://www.fabforce.net/dbdesigner4/screenshot_image.php?screenshot=dbd4_ss_simplemodel.png
seems like a nice quick way to model up databases for your projects. Thanks to "Mr. Perl" Dietrich Ayala ( http://dietrich.ganx4.com ) for the link.