Oracle SQL Developer Data Modeler
SQL Developer Data Modeler is a free data modeling and design tool, proving a full spectrum of data and database modeling tools and utilities, including modeling for Entity Relationship Diagrams (ERD), Relational (database design), Data Type and Multi-dimensional modeling, with forward and reverse engineering and DDL code generation. The Data Modeler imports from and exports to a variety of sources and targets, provides a variety of formatting options and validates the models through a predefined set of design rules.
View Demo on Oracle Website
http://download.oracle.com/otn_hosted_doc/sqldev/DataModeler30NewFeaturesOverview/DataModeler30NewFeaturesOverview.html