Generate an E-R Diagram by reverse-engineering a database

Note: Originally this question was asked for PostgreSQL, however, the answer applies to almost any database which has a JDBC driver that can detect foreign-key associations.

Querying PostgreSQL data dictionary for foreign-keys and relationship between tables is very straightforward, but how can I use that information to generate a graph of the relations between tables?

Any recommendations about tools that can do this?

EDIT: I know GraphVIZ/DOT can be useful, however, I don't know have any idea regarding how to code an app that would generate the directed graph .DOT file.