Many thanks to Radek Maciaszek who put together this roundup of data modelling tools:

 dbdesigner: http://www.fabforce.net/dbdesigner4
 + cross platform
 + reverse engineering
 + support postgresql by odbc
   (odbc: http://gborg.postgresql.org/project/psqlodbc/projdisplay.php)

zeos database designer: http://sourceforge.net/project/showfiles.php?group_id=35994
 + should be cross platform
 – doesn’t work on my system (crashes on startup)
Maybe it will work on yours?

azzuri: http://www.azzurri.jp/en/index.jsp
 ± commercial but with freeware version
 ± needs eclipse
 + reverse enginering
 + work with mysql and pgsql and with any jdbc sql’92 compatible db

dbmodeller: http://gborg.postgresql.org/project/dbmodeller/projdisplay.php
  + written in java (platform independent)
  + full source code available
  + reverse/forward engineering
  + mysql/postgresql/mssql/oracle
  – ugly

dbvisualiser: http://www.dbvis.com/products/dbvis/info.html 
  + java (platform independent)
  ± commercial but with freeware version
  + reverse engineering
  – problems with references 

DatabaseOrganizer: http://db-org.sourceforge.net/
  – needs tomcat
  + should work with mysql and postgresql

Abeille Personal Edition http://www.jetaware.com/Home.jsp
  ± commercial but with freeware version