dbViZ is a Java application that creates diagrams illustrating existing database schemas. Although similar to Entity-Relationship (ER) Diagrams, dbViZ diagrams show the schema as it is, without the abstraction, so you see exactly what tables and columns you need to use. This version is pretty stable and mainly suffers from a lack of UI convenience features.
See what dbViZ is all about at our homepage, which is temporarily at http://jdbv.sourceforge.net/dbViz