Let's not forget about PG Lightning Admin :-)
http://www.amsoftwaredesign.com
In case you don't like PgAdminIII you may try commercial products like
EMS PostgreSQL Manager http://sqlmanager.net/products/postgresql/manager
What they call "Visual Database Designer" might just be what you are looking for. It's an MS-Access-like, visual display of tables and relations. But remember, it's a frontend and not a modelling tool.
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